Semiconductor device and a method of manufacturing the same

ABSTRACT

A semiconductor device having a nonvolatile memory is reduced in size. In an AND type flash memory having a plurality of nonvolatile memory cells having a plurality of first electrodes, a plurality of word lines crossing therewith, and a plurality of floating gate electrodes disposed at positions which respectively lie between the plurality of adjacent first electrodes and overlap the plurality of word lines, as seen in plan view, the plurality of floating gate electrodes are formed in a convex shape, as seen in cross section, so as to be higher than the first electrodes. As a result, even when nonvolatile memory cells are reduced in size, it is possible to process the floating gate electrodes with ease. In addition, it is possible to improve the coupling ratio between floating gate electrodes and control gate electrodes of the word lines without increasing the area occupied by the nonvolatile memory cells.

This is a Continuation of application Ser. No. 10/902,141, filed Jul.30, 2004, now U.S. Pat. No. 7,064,380, the entire disclosures of whichare hereby incorporated by reference.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent applicationJP 2003-314648, filed on Sep. 5, 2003, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and to atechnique for the manufacture thereof. More particularly, it relates toa technique that is applicable to a semiconductor device having anonvolatile memory, such as an EEPROM (Electrically ErasableProgrammable Read Only Memory) or a flash memory, or a method ofmanufacturing the same.

A nonvolatile memory cell that was studied by the present inventors has,other than a floating gate electrode and a control gate electrode, athird gate electrode, which is referred to as an assist gate electrode.Over the principal surface of a semiconductor substrate, a plurality ofassist gate electrodes, each in the form of a band, as seen in planconfiguration, are arranged in such a manner as to abut one another. Inan insulating film covering the plurality of assist gate electrodes,trenches are formed between each of the adjacent assist gate electrodes,and a floating gate electrode, which is convex as seen in cross section,is provided on the side and bottom of each trench. Over the floatinggate electrode, a control gate electrode is provided via an interlayerfilm.

Incidentally, for example, Japanese Unexamined Patent Publication No.2000-188346, discloses an NAND type flash memory cell configured suchthat, between adjacent STI regions for isolation formed over theprincipal surface of a semiconductor substrate, a floating gateelectrode, which is convex as seen in cross section, is provided, and acontrol gate electrode is provided via an interlayer film in such amanner as to cover the surface. (Patent Document 1).

[Patent Document 1] Japanese Unexamined Patent Publication No.2000-188346

SUMMARY OF THE INVENTION

However, for a semiconductor device having a nonvolatile memory, thetrend toward miniaturization has increasingly advanced. Under suchcircumstances, how the device is reduced in size without causing variousdeficiencies is an important consideration.

It is an object of the present invention to provide a technology that iscapable of reducing the size of a semiconductor device having anonvolatile memory.

The foregoing and other object, and novel features of the presentinvention will be apparent from the following description in thisspecification and the appended drawings.

Out of the various aspects and features of the invention disclosed inthis application, an outline of typical ones will be briefly describedas follows.

In accordance with one aspect of the present invention, a semiconductordevice comprises: a semiconductor substrate; and a plurality ofnonvolatile memory cells having a plurality of first electrodes, aplurality of second electrodes provided so as to cross therewith, and aplurality of third electrodes for electric charge accumulation providedat points of intersection of the portions between the plurality of theadjacent first electrodes and the plurality of the second electrodes ina state insulated from the first and second electrodes, over thesemiconductor substrate, wherein the third electrodes are each formed ina convex shape as seen in cross section in such a manner as to be largerin height than the first electrodes.

Further, in accordance with another aspect of the present invention, asemiconductor device comprises: a semiconductor substrate; and aplurality of nonvolatile memory cells having a plurality of firstelectrodes, a plurality of second electrodes provided so as to crosstherewith, and a plurality of third electrodes for electric chargeaccumulation provided at points of intersection of the portions betweenthe plurality of adjacent first electrodes and the plurality of secondelectrodes in a state insulated from the first and second electrodes,over the semiconductor substrate, wherein the plurality of the firstelectrodes have a function of forming an inversion layer in thesemiconductor substrate.

The effects obtainable by typical features of the invention disclosed inthis application will be briefly described as follows.

It is possible to promote the trend for increased miniaturization of anonvolatile memory.

Further, it is possible to reduce the size of a semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a characteristic part of a semiconductor devicerepresenting one embodiment of the present invention;

FIG. 2 is a cross sectional view taken along line Y1-Y1 of FIG. 1;

FIG. 3 is a cross sectional view taken along line X1-X1 of FIG. 1;

FIG. 4 is a cross sectional view taken along line X2-X2 of FIG. 1;

FIG. 5 is a circuit diagram, during the data write operation, of thesemiconductor device of FIG. 1;

FIG. 6 is a cross sectional view of the semiconductor device during thedata write operation of FIG. 5;

FIG. 7 is a circuit diagram of the semiconductor device during the datawrite operation of FIG. 1;

FIG. 8 is a cross sectional view of the semiconductor device during thedata write operation of FIG. 7;

FIG. 9 is a cross sectional view of the semiconductor device during thedata erasing operation;

FIG. 10 is a plan view showing one example of a semiconductor substratein a step of manufacturing the semiconductor device of FIG. 1;

FIG. 11 is a cross sectional view taken along line Y1-Y1 of FIG. 10;

FIG. 12 is a cross sectional view taken along line X1-X1 of FIG. 10;

FIG. 13 is a cross sectional view showing one example of thesemiconductor substrate in a peripheral circuit region of thesemiconductor device in the manufacturing step of FIG. 10;

FIG. 14 is a plan view showing one example of the semiconductorsubstrate in a step of manufacturing the semiconductor device subsequentto the manufacturing step of FIG. 10;

FIG. 15 is a cross sectional view taken along line Y1-Y1 of FIG. 14;

FIG. 16 is a cross sectional view taken along line X1-X1 of FIG. 14;

FIG. 17 is a cross sectional view taken along line X2-X2 of FIG. 14;

FIG. 18 is a cross sectional view showing one example of thesemiconductor substrate in a peripheral circuit region of a flash memoryin the manufacturing step of FIG. 14;

FIG. 19 is a cross sectional view showing one example of the portioncorresponding to line Y1-Y1 of FIG. 14 of the semiconductor substrate ina step of manufacturing the semiconductor device subsequent to themanufacturing steps of FIG. 10 and the like;

FIG. 20 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 14 in the same step as that of FIG. 19;

FIG. 21 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 14 in the same step as that of FIG. 19;

FIG. 22 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of the flashmemory in the same step as that of FIG. 14;

FIG. 23 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 14 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 19;

FIG. 24 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 14 in the same step as that of FIG. 23;

FIG. 25 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 14 in the same step as that of FIG. 23;

FIG. 26 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 23;

FIG. 27 is a plan view of the semiconductor device in a manufacturingstep subsequent to the manufacturing step of FIG. 23 and the like;

FIG. 28 is a plan view on an enlarged scale of the semiconductor deviceof FIG. 27;

FIG. 29 is a cross sectional view taken along line Y1-Y1 of FIG. 28;

FIG. 30 is a cross sectional view taken along line X1-X1 of FIG. 28;

FIG. 31 is a cross sectional view taken along line X2-X2 of FIG. 28;

FIG. 32 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 27;

FIG. 33 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 28 in a manufacturing step subsequent to the manufacturingstep of FIG. 27;

FIG. 34 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 28 in the same step as that of FIG. 33;

FIG. 35 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 28 in the same step as that of FIG. 33;

FIG. 36 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 33;

FIG. 37 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 28 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 33;

FIG. 38 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 28 in the same step as that of FIG. 37;

FIG. 39 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 28 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 37 and the like;

FIG. 40 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 28 in the same step as that of FIG. 39;

FIG. 41 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 28 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 39;

FIG. 42 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 28 in the same step as that of FIG. 41;

FIG. 43 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 28 in the same step as that of FIG. 41;

FIG. 44 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 33;

FIG. 45 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 28 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 41;

FIG. 46 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 28 in the same step as that of FIG. 45;

FIG. 47 is a cross sectional view showing the portion corresponding toline X2-X2 of FIG. 28 in the same step as that of FIG. 45;

FIG. 48 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 45;

FIG. 49 is a plan view showing one example of the semiconductorsubstrate in a step of manufacturing the semiconductor device subsequentto the manufacturing step of FIG. 41;

FIG. 50 is a cross sectional view taken along line Y1-Y1 of FIG. 49;

FIG. 51 is a cross sectional view taken along line X1-X1 of FIG. 49;

FIG. 52 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 49;

FIG. 53 is a cross sectional view of the portion corresponding to lineY1-Y1 of FIG. 49 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 49 and the like;

FIG. 54 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 49 in the same step as that of FIG. 53;

FIG. 55 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 49 in the same step as that of FIG. 53;

FIG. 56 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 53;

FIG. 57 is a plan view of the semiconductor device in a manufacturingstep subsequent to the manufacturing step of FIG. 53;

FIG. 58 is a cross sectional view taken along line Y1-Y1 of FIG. 57;

FIG. 59 is a cross sectional view taken along line Y2-Y2 of FIG. 57;

FIG. 60 is a cross sectional view taken along line X1-X1 of FIG. 57;

FIG. 61 is a cross sectional view taken along line X2-X2 of FIG. 57;

FIG. 62 is a plan view of the semiconductor device in a manufacturingstep subsequent to the manufacturing step of FIG. 57;

FIG. 63 is a cross sectional view taken along line Y1-Y1 of FIG. 62;

FIG. 64 is a cross sectional view taken along line Y2-Y2 of FIG. 62;

FIG. 65 is a cross sectional view taken along line X1-X1 of FIG. 62;

FIG. 66 is a cross sectional view taken along line X2-X2 of FIG. 62;

FIG. 67 is a cross sectional view of one example of the semiconductorsubstrate in the peripheral circuit region of the semiconductor devicein the same step as that of FIG. 62;

FIG. 68 is a cross sectional view of the portion corresponding to lineY2-Y2 of FIG. 62 in a manufacturing step of the semiconductor devicesubsequent to the manufacturing step of FIG. 62;

FIG. 69 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 62;

FIG. 70 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 62 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 68;

FIG. 71 is a cross sectional view one example of the semiconductorsubstrate in the peripheral circuit region of the semiconductor devicein the same step as that of FIG. 70;

FIG. 72 is a cross sectional view of the portion corresponding to lineX1-X1 of FIG. 62 in a step of manufacturing the semiconductor devicesubsequent to the manufacturing step of FIG. 70;

FIG. 73 is a cross sectional view of the portion corresponding to lineX2-X2 of FIG. 62 in the same step as that of FIG. 72;

FIG. 74 is a cross sectional view showing one example of thesemiconductor substrate in the peripheral circuit region of thesemiconductor device in the same step as that of FIG. 72;

FIG. 75 is a cross sectional view showing the semiconductor device in amanufacturing step for illustrating a problem which has occurred in themanufacturing step of the semiconductor device of the present invention;

FIG. 76 is a cross sectional view showing the semiconductor device in amanufacturing step subsequent to the step of FIG. 75;

FIG. 77 is a cross sectional view showing the semiconductor device in amanufacturing step subsequent to the step of FIG. 76;

FIG. 78 is a plan view showing the semiconductor device of FIG. 77 in amanufacturing step;

FIG. 79 is a cross sectional view showing the semiconductor device in amanufacturing step for illustrating a problem which has occurred in themanufacturing step of the semiconductor device of the present invention;

FIG. 80 is a cross sectional view of the semiconductor device in amanufacturing step subsequent to the step of FIG. 79;

FIG. 81 is a cross sectional view of the semiconductor device in amanufacturing step subsequent to the step of FIG. 80;

FIG. 82 is a plan view of a semiconductor device representing anotherembodiment of the present invention;

FIG. 83 is a cross sectional view of the portion corresponding to lineX2-X2 of the semiconductor device of FIG. 82 in a manufacturing step;

FIG. 84 is a cross sectional view of the portion corresponding to lineX2-X2 of the semiconductor device in a manufacturing step subsequent tothe manufacturing step of FIG. 83;

FIG. 85 is a cross sectional view of the portion corresponding to lineX2-X2 of the semiconductor device in a manufacturing step subsequent tothe 10 manufacturing step of FIG. 84;

FIG. 86 is a cross sectional view of a memory region of a semiconductordevice which represents still another embodiment of the presentinvention;

FIG. 87 is a cross sectional view of a semiconductor substrate during adata write operation of the semiconductor device of FIG. 86;

FIG. 88 is a cross sectional view of the semiconductor substrate duringa data read operation of the semiconductor device of FIG. 86;

FIG. 89 is a cross sectional view of the semiconductor substrate duringa data erasing operation of the semiconductor device of FIG. 86;

FIG. 90 is a cross sectional view of a memory region of a semiconductordevice which represents a still further embodiment of the presentinvention;

FIG. 91 is a cross sectional view of a semiconductor substrate during adata write operation of the semiconductor device of FIG. 90;

FIG. 92 is a cross sectional view of the semiconductor substrate duringa data read operation of the semiconductor device of FIG. 90;

FIG. 93 is a cross sectional view of the semiconductor substrate duringa data erasing operation of the semiconductor device of FIG. 90; and

FIG. 94 is a plan view showing one example of the layout of a memory matof a semiconductor device which represents one embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, individual embodiments may be divided intoa plurality of sections or embodiments for the sake of convenience, ifnecessary. Except when otherwise specified, they are not mutuallyirrelevant, but one may be in the relation of a varied example, adetail, a supplemental statement, or the like of a part or the whole ofthe other. Further, in the following description, when reference is madeto numbers of elements and the like (including the number, numericalvalue, amount, range, and the like), except when otherwise specified,and except when such numbers are apparently limited to specific numbersin principle, they are not limited to the specific numbers, and may beeither equal to or larger than, or equal to or smaller than the specificnumbers. Still further, in the following description, it is understoodthat, the constituent elements (including elemental steps and the like)are not necessarily essential, except when otherwise specified, andexcept when they are presumed to be apparently essential in principle.Likewise, in the following embodiments, when reference is made to theshape and positional relationship of constituent elements, and the like,they are to be construed as including ones that are substantiallyanalogous or similar to the specified shape, and the like, except whenotherwise specified, and except when they are presumed to be apparentlynot so in principle. This is also true for the foregoing numericalvalues and ranges. Furthermore, in the case of the drawings, even a planview may be hatched in order to make features of the plan view easilyvisible. Further, throughout the drawings, the same elements areidentified with the same numerals and signs, and a repetitivedescription thereof will be omitted. Further, in the followingdescription, a MIS•FET (Metal Insulator Semiconductor•Field EffectTransistor), which is a field effect transistor, is abbreviated as anMIS, an n-channel type MIS is abbreviated as an nMIS, and a p-channeltype MIS is abbreviated as a pMIS. Below, the embodiments of the presentinvention will be described in detail by reference to the accompanyingdrawings.

Embodiment 1

In Embodiment 1, a description will be given of one example of the casewhere the present invention is applied to, for example, a 4-Gbit ANDtype flash memory unit.

FIG. 1 is a plan view of the flash memory of this embodiment 1; FIG. 2is a cross sectional view taken along line Y1-Y1 of FIG. 1; FIG. 3 is across sectional view taken along line X1-X1 of FIG. 1; and FIG. 4 is across sectional view taken along X2-X2 of FIG. 1. Incidentally, a sign Xin FIG. 1 denotes a first direction, and a sign Y in the same figuredenotes a second direction that is orthogonal to the first direction X.

A semiconductor substrate (hereinafter simply referred to as asubstrate) 1S of a semiconductor chip, in which the flash memory of thisembodiment 1 is formed, is made of, for example, a p type silicon (Si)single crystal. Over the principal surface (device-formed surface)thereof, there are arranged an active region 2, an isolation region 3, aplurality of first electrodes 4G, a plurality of word lines (secondelectrodes) 5, a plurality of floating gate electrodes (thirdelectrodes) 6G, a plurality of nonvolatile memory cells (hereinaftersimply referred to as memory cells) MC, and a plurality of selectingnMIS Qsn0 and selecting nMIS Qsn1. Referring to the cross section of thesubstrate 1S, a p type well PW1 and an n type buried region NISO areformed in the memory region and the selecting transistor region of thesubstrate 1S. The p type well PW1 is formed by introducing, for example,boron (B) therein, and the outer periphery (side and bottom) thereof issurrounded by the n type buried region NISO. In the n type buried regionNISO, for example, phosphorus (P) has been introduced.

The active region 2 is a region where a device is formed. As will bedescribed later, in the active region 2 in the memory region, asemiconductive region for a bit line is not formed, so that the memoryregion has been scaled down. The outline in plan configuration of theactive region 2 is defined by the isolation region 3. The isolationregion 3 is formed as a trench type isolation region referred to as, forexample, a STI (Shallow Trench Isolation) or a SGI (Shallow GrooveIsolation). Namely, the isolation region 3 is formed by burying aninsulating film such as a film of silicon oxide (SiO₂, or the like) in atrench dug in the substrate 1S.

The plurality of first electrodes 4G are each formed in the shape of arectangle extending along the first direction X as seen in planconfiguration. The respective first electrodes 4G are arranged roughlyin parallel to one another along the second direction Y at a desireddistance away from one another. The dimension (width) along the seconddirection Y of the narrow portion of the first electrode 4G is, forexample, about 65 nm. Whereas, the spacing between the adjacent firstelectrodes 4G is, for example, about 115 nm. The first electrode 4G isdisposed mostly in overlapping relation with the active region 2 as seenin plan view. When a desired voltage is applied to the first electrode4G, an n type inversion layer is formed in the principal surface portionof the substrate 1S in the active region 2 along the first electrode 4G.The n type inversion layer is a portion for forming a bit line (sourceand drain of a memory cell MC).

The mechanism whereby the source and the drain of the memory cell MC areelectrically connected to a global bit line and a common drain line,respectively, will be described below by reference to FIG. 4, which is across sectional view taken along line X2-X2 line and line X3-X3 ofFIG. 1. Herein, FIG. 4 shows a cross section taken along line X2-X2. Theconfigurations of the cross sections taken along line X2-X2 and X3-X3are symmetrically equal, except that an electrical connection isestablished to the global bit line or the common drain line. Therefore,a detailed description of the structure on line X3-X3 is omitted.

When a desired voltage is applied to a desired first electrode 4G, a bitline for a drain (an n type inversion layer) is formed in the activeregion 2 under the first electrode 4G shown in FIG. 1. As shown in FIG.4, an electrical connection is established to a desired selecting nMISQsn0 via an n⁻ type semiconductive region 7 formed in the principalsurface of the substrate 1S, which further establishes an electricalconnection to the common drain line via the selecting nMIS Qsn0. The n⁻type semiconductive region 7 is formed by introducing, for example,arsenic (As) between the first electrode 4G and a selecting nMIS Qsn0 onits extension line along the first direction X. Whereas, as describedabove, the same also holds for the connection between the source of thememory cell MC and the global bit line. Namely, each first electrode 4Gis provided in order to form the source region and the drain region ofthe memory cell MC.

Thus, in this embodiment 1, in the region where each memory cell MC isformed, an inversion layer for a bit line is formed by the firstelectrode 4G in the principal surface portion of the substrate 1S in theactive region 2. Therefore, a semiconductive region for forming a bitline is not formed in the active region 2. When the semiconductiveregion for forming a bit line is formed in the active region 2, theensuring of various dimensions becomes necessary, such as the ensuringof dimensions allowing for the impurity diffusion in a semiconductiveregion for forming a bit line, the ensuring of dimensions for implantingimpurity ions, and the ensuring of dimensions allowing for misalignment.This forces the size of the memory cell MC to be increased. In contrast,in this embodiment 1, a semiconductive region for a bit line is notformed in the region for forming each memory cell MC therein. For thisreason, it is possible to largely reduce the size of the memory cell MC,which enables a large reduction of the dimensions of the whole memoryregion. Further, the first electrode 4G has not only the function offorming a bit line, but also the function of providing isolation betweenthe adjacent memory cells MC. This eliminates the necessity of providinga trench type isolation region 3 in the memory region, which enables areduction of the pitch of the bit lines to be formed. Further, problemsof the stress imposed from the trench-type isolation region 3 due tominiaturization and the like do not arise. Still further, in forming theconfiguration in which the sources and the drains (bit lines) of theadjacent memory cells MC are shared, it is not necessary to form adiffusion layer by implantation of an impurity. Accordingly, aconfiguration is adopted in which the source and drain regions (bitlines) are formed by utilizing an inversion layer. For this reason, theproblems of thermal diffusion of impurities due to miniaturization andthe like do not arise. This enables a reduction of the area occupied bythe memory region.

In the unit region of the memory region, for example, four firstelectrodes 4G (G0 to G3) are disposed. Namely, the four first electrodes4G (G0 to G3) are taken as one set. FIG. 1 shows the followingsituation. At the right-hand side edge of one first electrode 4G (G1) inthe unit region, a broad region 4GA for connection with an upper layerwire is formed; at the left-hand side edge of the underlying adjacentfirst electrode 4G (G2), a broad region 4GA for connection with theupper layer wire is formed; the right-hand side edge of the underlyingadjacent first electrode 4G (G3) is connected to a wire 4LA; and theleft-hand side edge of the underlying adjacent first electrode 4G (G0)is connected to a wire 4LB. The wires 4LA and 4LB are each formed in aband-shaped pattern extending along the second direction Y of FIG. 1. Toeach of them, the first electrode 4G (G3 or G0), which is one of everyfour, is integrally connected. Namely, the wires 4LA and 4LB are eachconfigured as a common wire for a plurality of the first electrodes 4Gto which the same electric potential is supplied. Such first electrodes4G (G0 to G3), and 4GA, and wires 4LA and 4LB are formed by, forexample, patterning a low resistive polysilicon film during the samestep. Herein, from the viewpoint of ease in formation and the like, aplurality of the first electrodes 4G to which the same electricpotential is supplied, the broad regions 4GA, and the wires 4LA and 4LBare integrally formed to be in the same layer, and they are electricallyconnected to one another. The thickness of each of the first electrodes4G and the wires 4LA and 4LB is, for example, about 50 nm. Thus, byreducing the thickness of each first electrode 4G, it is possible toreduce the coupling ratio between the first electrode 4G and thefloating gate electrode 6G. This can reduce the height of the floatinggate electrode 6G. An insulating film 8 between the first electrodes 4Gand the wires 4LA and 4LB and the principal surface of the substrate 1Sis formed of, for example, silicon oxide, and it has a thickness of, forexample, about 8.5 nm in terms of the silicon dioxide equivalent filmthickness. Over all sides of the first electrodes and one side of eachof the wires 4LA and 4LB, an insulating film 9 is formed of, forexample, silicon oxide. Whereas, over the top surfaces of the firstelectrodes 4G and the wires 4LA and 4LB, a cap film 10 is formed of, forexample, silicon nitride (Si₃N₄, or the like). Further, over the capfilm 10 of the first electrodes 4G in the outer periphery of the memoryregion, the broad regions 4GA, and the wires 4LA and 4LB, an insulatingfilm 11 formed of, for example, silicon oxide is deposited. Further, asits overlying layer, an insulating film 12 formed of, for example,silicon oxide is deposited. Each first electrode 4G is electricallyconnected to its corresponding upper first layer wire M1 via a plug PGin a contact hole CT. The contact holes CT are opened in the cap film 10and the insulating films 11 and 12, and they are disposed in a part ofthe broad regions 4GA and the wires 4LA and 4LB.

The number of the plurality of the word lines 5 (WL) formed per block ofmemory cells (memory mat) is 256. In this embodiment, for easyunderstanding of the description, WL0 to WL2 are shown. The respectiveword lines 5 (WL0 to WL2) are each formed in a rectangle extending alongthe second direction Y in plan configuration. Namely, the respectiveword lines 5 (WL0 to WL2) are disposed in a state orthogonal to thefirst electrodes 4G (G0 to G3) and in roughly parallel alignment withone another at a desired distance away from one another along the firstdirection X of FIG. 1. Each portion of the word lines 5 situated betweenthe adjacent first electrodes 4G serves as a control gate electrode ofthe memory cell MC. The dimension along the first direction X of theword line 5 on design is equal to the spacing between the adjacent wordlines 5 on design, and it is, for example, about 90 nm. Thus, by makingthe dimension along the first direction X of the word line 5 on designequal to the spacing between the adjacent word lines 5 on design, it ispossible to facilitate the calculation of the coupling ratio between thecontrol gate electrode 5 a and the floating gate electrode 6G.Accordingly, it becomes possible to set the coupling ratio at a bettervalue. Namely, it is possible to maximize the coupling ratio between thecontrol gate electrode 5 a and the floating gate electrode 6G. Each wordline 5 is formed of, for example, a multilayered film consisting of aconductor film 5 a made of a low resistive polysilicon and a refractorymetal silicide film 5 b, such as a film of tungsten silicide (WSi_(x))formed on the top surface thereof. Over the top surfaces of the wordlines 5, an insulating film 13 formed of, for example, silicon oxide isdeposited. Incidentally, both of the outermost word lines 5 along thefirst direction X are each configured in a pattern not contributing tothe memory operation, and they are formed to be broader than the otherword lines 5 in consideration of thinning upon exposure. Whereas, asshown in the cross sectional view of FIG. 2, the conductor film 5 a,which is the lower layer of the word line 5, is formed in such a manneras to be buried between the respective floating gate electrodes 6G viathe insulating film 18 in the direction Y of the respective memory cellsMC.

The plurality of floating gate electrodes 6G are disposed at the pointsof intersection of the portions between the adjacent first electrodes 4G(G0 to G3) and the word lines 5 (WL0 to WL2) in an electricallyinsulated state. The floating gate electrode 6G is an electric chargeaccumulation layer for data of the memory cells MC, and it is formed of,for example, a low resistive polysilicon. Each floating gate electrode6G has the form of a rectangle as seen in plan view. The dimension alongthe first direction X of the floating gate electrode 6G is roughly equalto the dimension along the first direction X of the word line 5. It isset at, for example, about 90 nm. The dimension along the seconddirection Y of the floating gate electrode 6G is slightly shorter thanthe spacing between the adjacent first electrodes 4G, and it is set at,for example, about 65 nm.

Whereas, the floating gate electrodes 6G are, as seen in a crosssection, provided over the principal surface of the substrate 1S via aninsulating film 15. The insulating film 15 functions as a tunnelinsulating film of the memory cells MC, and it is formed of, forexample, silicon oxynitride (SiON), or the like. The silicon oxynitridefilm has a configuration in which nitrogen (N) has been segregated atthe interface between silicon oxide and the substrate 1S. The insulatingfilm 15 may be formed of, for example, silicon oxide. However, byforming the insulating film 15 with silicon oxynitride, it is possibleto improve the reliability of the insulating film 15. Namely, by linkingnitrogen to an unstable bond, trap level, or the like, formed in theprincipal surface of the substrate 1S due to damage or the like imposedon the substrate 1S before the formation of the insulating film 15, itis possible to improve the reliability of the insulating film 15. Thethickness of the insulating film 15 is set at, for example, about 9 nmin terms of the silicon dioxide equivalent film thickness.

Between the floating gate electrodes 6G and the first electrodes 4G, theinsulating films 9 and 16 are formed, which insulates the firstelectrodes 4G from the floating gate electrodes 6G. Whereas, between theadjacent floating electrodes 6G and the adjacent word lines 5 along thefirst direction X, an insulating film 17 is formed. This insulatesbetween the adjacent floating electrodes 6G and the adjacent word lines5 along the first direction X. The insulating films 16 and 17 are madeof, for example, silicon oxide. Further, between the floating gateelectrodes 6G and the control gate electrodes of the word lines 5, aninsulating film 18 is formed. The insulating film 18 is a film forforming capacitors between the floating gate electrodes 6G and thecontrol gate electrodes. It is formed of, for example, a so-called ONOfilm prepared by laminating silicon oxide, silicon nitride, and siliconoxide, sequentially from the bottom layer. The thickness of theinsulating film 18 is set at, for example, about 16 nm in terms of thesilicon dioxide equivalent film thickness.

As shown in FIG. 2 or 3, in this embodiment 1, the floating gateelectrodes 6G are each formed in a convex shape (herein, in the shape ofa rectangle) as seen in cross section along the direction crossing withthe principal surface of the substrate 1S. They are each formed in ashape protruding from the surface of the semiconductor substrate 1S.Namely, the floating gate electrodes 6G are formed each in the shape ofa pole (herein, in the shape of a square pole) in the regions interposedbetween the first electrodes 4G over the semiconductor substrate 1S viathe insulating film 15. The floating gate electrodes 6G are each formedin such a manner that it's the height thereof (the height from theprincipal surface of the substrate 1S) becomes larger than the height(the height from the principal surface of the substrate 1S) of eachfirst electrode 4G. When each floating gate electrode is formed in aconcave shape, the floating gate electrode must be reduced in thicknesswith the reduction in size of a memory cell. As in this and other cases,it becomes difficult to process the floating gate electrode. Incontrast, in this embodiment 1, each floating gate electrode 6G isformed in a convex shape in cross section. As a result, even when thememory cell MC is reduced in size, it is possible to process thefloating gate electrode 6G with ease. For this reason, it is possible topromote the reduction in size of the memory cells MC. Whereas, thecapacitors between the floating gate electrodes 6G and the control gateelectrodes are formed over the convex sidewalls and the convex topsurfaces of the floating gate electrodes 6G. Namely, the capacitance isformed between the word lines 5 (5 a) and the floating gate electrodes6G in the direction (Y-Y direction) in which the word lines 5 extend viaan insulating film 18. The capacitance is calculated as the sum of thevalues of the capacitances formed over the top surfaces and thesidewalls of the convex floating gate electrodes 6G. Therefore, evenwhen the minimum processing dimensions are further reduced, the floatinggate electrode 6G can be increased in height to increase the area ofopposing portions of the floating gate electrode 6G and the control gateelectrode, resulting in an increase in capacitance of the capacitorwithout increasing the area occupied by the memory cell MC. Therefore,it is possible to improve the coupling ratio between the floating gateelectrode 6G and the control gate electrode. For this reason, it ispossible to improve the controllability of voltage control of thefloating gate electrode 6G by the control gate electrode. This enablesan improvement in the writing and erasing speed of a flash memory evenat a low voltage, which allows the flash memory to be capable oflow-voltage operation. Namely, it is possible to implement both theminiaturization and the reduction in voltage of the flash memory. Theheight H1 of the floating gate electrode 6G (the height from the topsurface of the insulating film 12) is, for example, about 270 to 300 nm.The protrusion height H2 of the floating gate electrode 6G (the heightfrom the top surface of the insulating film 18 over the first electrodes4) is, for example, about 190 nm.

Herein, when the reduction in size of each memory cell MC proceeds, thelength of each floating gate electrode 6G along the direction (Y-Ydirection) in which the word line 5 extends is also reduced. In thiscase, the capacitance at the top surface portion of the floating gateelectrode 6G decreases with the reduction in size. However, in thisembodiment, an increase in height of the floating gate electrode 6Genables an increase in capacitance at the sidewall portion of thefloating gate electrode 6G. For this reason, it is possible to preventthe reduction in capacitance between the word lines 5 and the floatinggate electrodes 6G. Therefore, in order to prevent a reduction incapacitance due to a reduction in size, the device is preferablydesigned such that the height (H1) of each floating gate electrode 6G isinvariably larger than the length of the floating gate electrode 6Galong the direction (Y-Y direction) in which the word line 5 extends.The device is more preferably designed such that the protrusion height(H2) of the floating gate electrode 6G is invariably larger than thelength of the floating gate electrode 6G. The above description wasdirected to a case involving a reduction in size. However, needless tosay, it is also possible to further improve the capacitance in thesemiconductor device of this embodiment by designing the device suchthat the height (H1) and the protrusion height (H2) of the floating gateelectrode 6G are invariably larger than the length of the floating gateelectrode 6G.

Further, when the width of the first electrode 4G in the direction (Y-Ydirection) in which the word line 5 extends also has been reduced, thespace between the respective floating gate electrodes 6G adjacent to oneanother via the first electrodes 4G is also reduced. In this case, itmay become difficult to bury the insulating film 18 and the word lines 5(5 a) in the space between the respective floating gate electrodes 6G.In such a case, it is conceivable that the thickness of the insulatingfilm 18 is controlled, thereby to be reduced in thickness and to beburied. However, the capacitance between the word lines 5 and thefloating gate electrodes 6G is unfavorably reduced. Therefore, thecapacitance is required to be increased by the amount of the capacitancereduced due to the reduction in thickness of the insulating film 18through an increase in the height of the floating gate electrode 6G.Namely, in order to prevent a reduction in the capacitance due to areduction in size, for example, the device is preferably designed suchthat the height (H1) of each floating gate electrode 6G is invariablylarger than the spacing between the respective floating gate electrodes6G in the direction (Y-Y direction) in which the word lines 5 extend.The device is more preferably designed such that the protrusion height(H2) of the floating gate electrode 6G is invariably larger than thespacing between the respective floating gate electrodes 6G. Whereas, theabove description was directed to a case involving a reduction in size,needless to say, it is also possible to further improve the capacitancein the semiconductor device of this embodiment by designing the devicesuch that the height (H1) and the protrusion height (H2) of the floatinggate electrode 6G are invariably larger than the spacing between therespective floating gate electrodes 6G.

Whereas, in this embodiment, the length along the direction (Y-Ydirection) in which the word line extends of each floating gateelectrode 6G is roughly about the same as the length along the direction(X-X direction) in which the first electrode 4G extends. However, bydesigning the device such that the length along the direction (X-Xdirection) of extension of the first electrode 4G is larger than thelength of the floating gate electrode 6G along the direction (Y-Ydirection) of extension of the word lines, it is possible to increasethe value of the capacitance formed at the top surface portion and thesidewall portion of each floating gate electrode 6G. Particularly, it ispossible to increase the capacitance value of the sidewall portion.

The plurality of selecting nMIS Qsn are disposed on the side of a bitline serving as a drain of the memory cell MC and on the side of a bitline serving as a source thereof. On the bit line side serving as adrain in FIG. 1, each selecting nMIS Qsn0 is disposed for every bit linealong the second direction Y on the right-hand side of FIG. 1. Whereas,on the bit line side serving as a source, each selecting nMIS Qsn1 isdisposed for every bit line along the second direction Y on theleft-hand side of FIG. 1. Herein, a description will be given of the bitline side serving as a drain. However, the bit line side serving as asource is similar in configuration, and hence a description thereon isomitted.

As shown in FIG. 1, each gate electrode 4LC1 of the selecting nMIS Qsn0on the bit line side serving as a drain is formed at a part of aband-shaped wire 4LC extending along the second direction Y in such amanner as to be positioned along the wire 4LA (the portion crossing withthe band-shaped region of the active region 2). As for the selectingnMIS Qsn1 on the bit line side serving as a source, a wire 4LD1 servingas a gate electrode is formed at a part of a band-shaped wire 4LDextending along the second direction Y in such a manner as to bepositioned along the wire 4LB (the portion crossing with the band-shapedregion of the active region 2). The gate electrode 4LC1 and the wires4LC, 4LD1, and 4LD are formed of, for example, a low resistivepolysilicon film. These are formed by patterning simultaneously with thepatterning for the first electrodes 4G, the broad regions 4GA, and thewires 4LA and 4LB.

As shown in FIG. 4, on the gate electrode 4LC1 and the wire 4LC, a capfilm 10 is deposited. The gate electrode 4LC1 and the wire 4LC areelectrically connected to an upper first layer wire Ml through a plug PGin a contact hole CT. A gate insulating film 21 of respective selectingnMIS Qsn is formed of, for example, silicon oxide, and it is formedbetween the gate electrodes 4LC1 and the substrate 1S. Whereas, onesemiconductive region 22 a for the source and drain of each selectingnMIS Qsn is formed of the aforesaid n⁻ type semiconductive region 7 forbit line connection. The other semiconductive region 22 b for the sourceand drain of each selecting MIS Qsn has: an n⁻ type semiconductiveregion 22 b 1 formed in the vicinity of the edge of the gate electrode4LC1, and an n⁺ type semiconductive region 22 b 2 formed away from theedge of the gate electrode 4LC1 by the length of the n⁻ typesemiconductive region 22 b 1, and having a higher concentration thanthat of the n⁻ type semiconductive region 22 b 1. The semiconductiveregions 22 a and 22 b have been doped with, for example, arsenic (As).

As shown in FIG. 94, in each block (memory mat), one selecting nMIS Qsn0is provided per a plurality of memory cells MC on the side of a bit linefor a drain. It is configured such that the bit line BL (common drainline CD), serving as a drain of each block, is supplied with powerthrough a contact hole CT, and it is shared through a second wiringlayer M2 (not shown). Whereas, one selecting nMIS Qsn1 is provided per aplurality of memory cells MC on the side of a bit line for a source.This is, as described later, for the purpose of preventing respectiveglobal bit lines GBL of the adjacent blocks (memory mats) from beingshared.

Namely, these respective memory mats are formed in such a manner as toinclude, at least, a plurality of memory cells, drain bit line selectingnMIS Qsn0, and source bit line selecting nMIS Qsn1. Respective memorymats are arranged symmetrically with respect to the contact holes forsupply of power to a bit line for a drain or the contact holes forsupply of power to a bit line for a source. By arranging respectivememory mats in this manner, it is possible to share the contact holesfor supply of power to a bit line for a drain or for a source.Therefore, it is possible to more greatly reduce the area occupied bythe flash memory as compared with the case where memory mats having thesame configuration are arranged.

Now, an example of the write, read, and erasing operations of the flashmemory of this embodiment 1 will be described.

FIG. 5 shows a circuit diagram of the semiconductor device during a datawrite operation by constant charge injection. FIG. 6 shows a crosssectional view of the substrate 1S during a data write operation byconstant charge injection. As described above, the unit region isconfigured as follows: only one stage of the selecting nMIS Qsn01 (4LC)or the selecting nMIS Qsn02 is disposed on the common drain side; andthe first electrodes 4G are composed of 4 systems (G0 to G3). To theaforesaid global bit lines GBL0 to GBL3, selecting nMIS Qsn11 areprovided, respectively. Selecting nMIS Qsn12 are disposed at global bitlines GBL0′ to GBL3′ of the adjacent block. These selecting nMIS Qsn11or selecting nMIS Qsn12 are selected to be turned ON. As a result, theglobal bit lines GBL0 to GBL3 or GBL0′ to GBL3′ are supplied with asource electric potential. Then, a desired first electrode 4G out of thefirst electrodes 4G (G0 to G3) is supplied with a voltage, thereby toselect a desired memory cell MC.

Data writing is carried out according to a source side hot electroninjection method by source side selection and constant charge injection,with non-selected memory cells MC put in the through state. This enablesefficient data writing at a high speed and with a low current. Whereas,individual memory cells MC are capable of storing multilevel data. Themultilevel storage is carried out in the following manner. The writevoltage of the word line WL is set constant, and the write time ischanged. As a result, the amount of hot electrons to be injected to thefloating gate electrode 6G is changed. Therefore, it is possible to forma memory cell MC having several kinds of threshold value levels. Namely,the memory cell MC can store four or more values such as“00”/“01”/“10”/“11”. For this reason, one memory cell MC is capable ofimplementing an operation equivalent to those of two memory cells MC.Accordingly, it is possible to implement a reduction in the size of aflash memory.

In the data write operation, the word line WL0 (5) to which the selectedmemory cell MC is connected is supplied with a voltage of, for example,about 15 V, and other word lines WL1 (5), and the like are supplied witha voltage of, for example, 0V. Whereas, the first electrode G0 (4G) forforming the source of the selected memory cell MC is supplied with avoltage of, for example, about 1 V. The first electrode G1 (4G) forforming the drain of the selected memory cell MC is applied with avoltage of, for example, about 7 V. As a result, an n type inversionlayer 23 a for forming the source is formed in the principal surfaceportion of the substrate 1S facing the first electrode G0 (4G), and an ntype inversion layer 23 b for forming the drain is formed in theprincipal surface portion of the substrate 1S facing the first electrodeG1 (4G). By supplying the other first electrodes G2 (4G) and G3 (4G)with a voltage of, for example, 0V, an inversion layer is prevented frombeing formed in the principal surface portion of the substrate 1S facingthe first electrodes G2 (4G) and G3 (4G). This causes an isolationbetween the selected and non-selected memory cells MC. In this state,the wire 4LC is supplied with a voltage of, for example, 7V, thereby toturn ON the selecting nMIS Qsn0. Thus, a voltage of about 4V that isapplied to the common drain line CD is supplied to the drain of theselected memory cell MC through the n⁻ type semiconductive region 7 andthe n type inversion layer 23 b. However, still under this situation,the non-selected memory cells MC connected to the word line WL0 (5) arealso brought into the same state as that of the selected memory cell MC,so that data is also written in the non-selected memory cells MC. Suchbeing the situation, the global bit line GBL0 to which the inversionlayer 23 a for forming the source of the selected memory cell MC isconnected is supplied with a voltage of, for example, 0V. On the otherhand, the global bit line GBL2 to which the n type inversion layer 23 afor forming the source of the non-selected memory cell MC is connectedis supplied with a voltage of, for example, about 1.2 V. Whereas, theother global bit lines GBL1 and GBL2 are supplied with a voltage of, forexample, 0V. This causes a write current I1 to flow from the draintoward the source through the selected memory cell MC. At this step, theelectric charges accumulated in the n type inversion layer 23 a on thesource side are allowed to flow as a given constant channel current, andthey are injected into the floating gate electrode 6G with efficiencyvia the insulating film 15 (constant charge injection method). As aresult, data is written into the selected memory cell MC at a highspeed. On the other hand, a drain current is prevented from flowing fromthe drain toward the source through the non-selected memory cells MC, sothat data writing is inhibited. Incidentally, a symbol F in FIG. 5denotes the floating state, and an arrow C1 of FIG. 6 schematicallyshows the manner in which the electric charges for data are injected.

FIG. 7 shows a circuit diagram of the semiconductor device during a dataread operation, and FIG. 8 shows a cross sectional view of the substrate1S during a data read operation.

In data reading, the direction of a read current 12 is opposite to thecurrent direction during the write operation. Namely, the read current12 flows from the global bit lines GBL0 and GBL2 to the common drainline CD. In a data read operation, the word line WL0 (5) to which theselected memory cell MC is connected is supplied with a voltage of, forexample, about 2 to 5 V, and the other word lines WL1(5) and the likeare supplied with a voltage of, for example, 0V. Whereas, by supplyingthe first electrodes G0 (4G) and G1 (4G) for forming the source and thedrain of the selected memory cell MC with a voltage of, for example,about 5 V, an n type inversion layer 23 a for a source is formed in theprincipal surface portion of the substrate 1S facing the first electrodeG0 (4G), and an n type inversion layer 23 b for a drain is formed in theprincipal surface portion of the substrate 1S facing the first electrodeG1 (4G). Whereas, by supplying the other first electrodes G2 (4G) and G3(4G) with a voltage of, for example, 0V, an inversion layer is preventedfrom being formed in the principal surface portion of the substrate 1Sfacing the first electrodes G2 (4G) and G3 (4G). Thus, isolation iscarried out. At this step, the global bit lines GBL0 and GBL2 to whichthe n type inversion layer 23 a for a source of the selected memory cellMC is connected is supplied with a voltage of, for example, about 1V. Onthe other hand, the other global bit lines GBL1 and GBL3 are suppliedwith a voltage of, for example, 0 V. In this state, the wire 4LC issupplied with a voltage of, for example, about 3V, thereby to turn ONthe selecting nMIS Qsn. Thus, a voltage of about 0V that is applied tothe common drain line CD is supplied to the drain of the selected memorycell MC through the n⁻ type semiconductive region 7 and the n typeinversion layer 23 b. Data reading of the selected memory cell MC isperformed in this manner. FIG. 7 schematically shows the state in whichone bit is concurrently read out to 4 bits. At this step, the state ofthe accumulated electric charges of the floating gate electrode 6Gchanges the threshold voltage of the selected memory cell MC. For thisreason, it is possible to judge the data of the selected memory cell MCaccording to the state of the current flowing between the source and thedrain of the selected memory cell MC. For example, in the case of thetwo selected memory cells MC shown in FIG. 7, it is assumed that thethreshold value level of the left-hand side selected memory cell MC is 4V, and that the threshold value level of the right-hand side selectedmemory cell MC is 5V. In this case, when the read voltage is 5 V, acurrent flows through both the memory cells MC. However, when reading isperformed at 4.5 V, a current does not flow to the left-hand side cell,but a current flows through the right-hand cell. Thus, it is possible tocarry out a read operation on the multilevel storage memory cellaccording to the state of electric charges accumulated in the memorycell MC and the read voltage.

FIG. 9 shows a cross sectional view of the substrate 1S during a dataerasing operation. In a data erasing operation, a word line 5 to beselected is supplied with a negative voltage, thereby to cause F-N(Fowlor Nordheim) tunnel emission from the floating gate electrode 6G tothe substrate 1S. Namely, the word line 5 to be selected is suppliedwith a voltage of, for example, about −16 V. On the other hand, thesubstrate 1S is applied with a positive voltage. The first electrode 4Gis supplied with a voltage of, for example, 0V, so that an n typeinversion layer is not formed. This causes the electric charges for dataaccumulated in the floating gate electrode 6G to be emitted into thesubstrate 1S via the insulating film 15. Thus, the data of a pluralityof the memory cells MC are erased by one operation. Incidentally, FIG. 9schematically shows the manner in which the electric charges for dataare emitted.

Next, one example of a method of manufacturing the flash memory of thisembodiment 1 will be described by reference to FIGS. 10 to 74.

FIG. 10 is a plan view showing one example of the substrate 1S after astep of forming the active region 2 and the isolation region 3. FIG. 11is a cross sectional view taken along line Y1-Y1 of FIG. 10. FIG. 12 isa cross sectional view taken along line X1-X1 of FIG. 10. FIG. 13 is across sectional view of the substrate 1S in the peripheral circuitregion of the flash memory during the manufacturing step of FIG. 10.FIG. 10 is a plan view, wherein the isolation region 3 is hatched forconvenient reference in the drawing. The substrate 1S (at this step, asemiconductor wafer circular in plan view (which is hereinafter simplyreferred to as a wafer)) is made of, for example, a p type siliconsingle crystal. Over the principal surface (device-formed surface)thereof, the active region 2 and the trench type isolation region 3 areformed. The active region 2 is a region where devices are formed. Asshown in FIG. 10, it has a central rectangular region 2 a, and aplurality of band-shaped regions 2 b extend outwardly from theoppositely facing sides of the rectangular region 2 a in the firstdirection X. In this rectangular region 2 a, the plurality of memorycells MC and the inversion layer for a bit line are formed. In theband-shaped region 2 b, the inversion layer for a bit line is formed.Over the principal surface of the substrate 1S in the active region 2,an insulating film 25 made of, for example, silicon oxide is formed. Thetrench type isolation regions 3 for defining the outline of the planconfiguration of the active region 2 are formed by embedding aninsulating film made of, for example, silicon oxide, in the trenches dugin the principal surface of the substrate 1S.

FIG. 14 is a plan view of one example of the substrate 1S during amanufacturing step of the flash memory subsequent to the manufacturingsteps of FIG. 10. FIG. 15 is a cross sectional view taken along lineY1-Y1 of FIG. 14. FIG. 16 is a cross sectional view taken along lineX1-X1 of FIG. 14. FIG. 17 is a cross sectional view taken along lineX2-X2 of FIG. 14. FIG. 18 is a cross sectional view of one example ofthe substrate 1S in the peripheral circuit region of the flash memoryduring the manufacturing step of FIG. 14.

First, for example, phosphorous (P) is selectively introduced into thememory region of the substrate 1S by a conventional ion implantationmethod, or the like. As a result, an n type buried region NISO isformed. Then, for example, boron (B) is selectively introduced into thememory region and the peripheral circuit region of the substrate 1S by aconventional ion implantation method, or the like. As a result, a p typewell PW1 is formed. Whereas, for example, phosphorus is selectivelyintroduced into the peripheral circuit region of the substrate 1S. As aresult, an n type well NW1 is formed.

Thereafter, as shown in FIGS. 14 to 17, such a photoresist pattern(which is hereinafter simply referred to as a resist pattern) as toexpose the formation region of the n⁻ type semiconductive region 7 andto cover the other region is formed. Then, by the use of it as a mask,for example, arsenic is introduced into the substrate 1S by an ionimplantation method, or the like. As a result, the n⁻ typesemiconductive region 7 for connecting the memory cell MC with theselecting MOS Qsn is formed in the principal surface of the substrate1S. Incidentally, at this stage, the first electrode 4G, the wires 4LA,4LB, 4LC, and the like are not formed. However, in FIG. 4, the firstelectrode 4G, the wires 4LA, 4LB, 4LC, and the like are indicated bydashed lines for convenience of understanding the relative position atwhich the resist pattern RP1 is formed.

FIG. 19 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 14 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 14. FIG. 20 is a crosssectional view of a portion corresponding to line X1-X1 of FIG. 14during the same step as FIG. 19. FIG. 21 is a cross sectional view of aportion corresponding to line X2-X2 of FIG. 14 during the same step asFIG. 19. FIG. 22 shows a cross sectional view of one example of thesubstrate 1S in the peripheral circuit region of the flash memory duringthe same step as FIG. 19. Herein, first, over the principal surface ofthe substrate 1S (wafer), an insulating film (first insulating film) 8made of, for example, silicon oxide, is formed so as to have a thicknessof, for example, about 8.5 nm in terms of the silicon dioxide equivalentfilm thickness by a thermal oxidation method such as an ISSG (In-SituSteam Generation) oxidation method. Then, a conductor film 4 made of,for example, a low resistive polysilicon is deposited thereon so as tohave a thickness of, for example, about 50 nm by a CVD (Chemical VaporDeposition) method, or the like. A cap film (second insulating film) 10made of, for example, silicon nitride is further deposited thereon so asto have a thickness of, for example, about 70 nm by a CVD method or thelike. Subsequently, on the cap film 10, an insulating film (thirdinsulating film) 11 made of, for example, silicon oxide, is deposited bya CVD method using, for example, TEOS (Tetraethoxysilane) gas, or thelike. Then, a hard mask film 26 a made of, for example, a low resistivepolysilicon, is deposited thereon by a CVD method or the like. Anantireflection film 27 a made of, for example, silicon oxynitride (SiON)is further deposited thereon by a plasma CVD method or the like.Thereafter, on the antireflection film 27 a, a resist pattern RP2 forforming the first electrodes 4G is formed. In an exposure processing forthe formation of the resist pattern RP2, a Levenson type phase shiftmask is used as a photomask. Namely, a phase shift mask is used whichhas a configuration such that the phases of lights which have passedthrough transmission regions adjacent to each other are inverted by 180degrees relative to each other. Then, by the use of the resist patternRP2 as an etching mask, the portions of the antireflection film 27 a andthe hard mask film 26, exposed therefrom, are etched, followed byremoval of the resist pattern RP2. The states of the flash memory duringthe manufacturing steps subsequent to this step are shown in FIGS. 23 to26.

FIG. 23 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 14 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 19. FIG. 24 is a crosssectional view of a portion corresponding to line X1-X1 of FIG. 14during the same step as FIG. 23. FIG. 25 is a cross sectional view of aportion corresponding to line X2-X2 of FIG. 14 during the same step asFIG. 23. FIG. 26 shows a cross sectional view of one example of thesubstrate 1S in the peripheral circuit region of the flash memory duringthe same step as FIG. 23. Herein, the pattern of the antireflection film27 a and the hard mask film 26 a for forming the first electrodes isformed by etching processing. Subsequently, by the use of theantireflection film 27 a and the hard mask film 26 a as an etching mask,the portions of the insulating film 11, the cap film 10, and theconductor film 4, exposed therefrom, are etched. The states of the flashmemory during the manufacturing steps subsequent to this step are shownin FIGS. 27 to 32.

FIG. 27 is a plan view of the flash memory during a manufacturing stepof the flash memory subsequent to the manufacturing step of FIG. 23.FIG. 28 is a plan view on an enlarged scale of the device of FIG. 27.FIG. 29 is a cross sectional view taken along line Y1-Y1 of FIG. 28.FIG. 30 is a cross sectional view taken along line X1-X1 of FIG. 28.FIG. 31 is a cross sectional view taken along line X2-X2 of FIG. 28.FIG. 32 shows a cross sectional view of one example of the substrate 1Sin the peripheral circuit region of the flash memory during the samestep as FIG. 27. Herein, the first electrodes 4G and the broad regions4GA are formed through patterning by the etching processing of theconductor film 4. At this step, the dimension along the width direction(the dimension along the second direction Y of FIG. 27, 28, and thelike) of each first electrode 4G is, for example, about 75 nm. Thespacing along the second direction Y between the adjacent firstelectrodes 4G is, for example, about 105 nm. With the etching processingof the conductor film 4, the side of each trench 28 in the etchingregion, i.e., the side of each pattern of a multilayered film of theleft first electrodes 4G, cap film 10, and insulating film 11, ispreferably as vertical as possible with respect to the principal surfaceof the substrate 1S. The reason for this will be described later. Withthe etching processing, when the insulating film 11 and the cap film 10are etched, the antireflection film 27 a is etched. Whereas, when theconductor film 4 is etched, the hard mask film 26 a is etched.Therefore, after the etching processing, the antireflection film 27 aand the hard mask film 26 a are not left.

FIG. 33 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 28 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 28. FIG. 34 is a crosssectional view of a portion corresponding to line X1-X1 of FIG. 28during the same step as FIG. 33. FIG. 35 is a cross sectional view of aportion corresponding to line X2-X2 of FIG. 28 during the same step asFIG. 33. FIG. 36 shows a cross sectional view of one example of thesubstrate 1S in the peripheral circuit region of the flash memory duringthe same step as FIG. 33. Herein, into the region where the firstelectrode 4G and the conductor film 4 are not present on the principalsurface portion of the substrate 1S (wafer), an impurity such as boronis introduced by a conventional ion implantation method or the like. Atthis step, as shown in FIG. 35, boron is also introduced into a part ofthe n⁻ type semiconductive region 7 of a connecting part between thefirst electrode 4G and the selecting transistor region. However, theamount of boron to be introduced is about one order smaller than theamount of the impurity to be introduced into the n⁻ type semiconductiveregion 7. For this reason, it is possible to ensure the continuity ofthe electric current path of the n⁻ type semiconductive region 7. Thisimpurity introducing processing is used for causing a difference betweenthe threshold voltage at the substrate 1S under the first electrode 4Gand the threshold voltage at the substrate 1S under the floating gateelectrode 6G. By this processing, the p type impurity concentrationunder the floating gate electrode 6G becomes higher than the p typeimpurity concentration of the first electrode 4G. Therefore, thethreshold voltage at the substrate 1S under the first electrode 4G, witha relatively low p type impurity concentration, becomes lower than thethreshold voltage at the substrate 1S under the floating gate electrode6G. Incidentally, the boron introducing step need not be performed insome cases. A study conducted by the present inventors has proved thatthe flash memory normally operates either with or without theintroduction of boron. Alternatively, it is also possible to carry outthe boron introducing step after the formation of an insulating film 16(sidewalls in the periphery) to be described later.

Subsequently, the substrate 1S is subjected to a thermal oxidationprocessing, such as an ISSG oxidation method. The states of the devicein manufacturing steps subsequent to this step are shown FIGS. 37 and38. FIG. 37 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 28 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 33 and the like. FIG. 38shows a cross sectional view of a portion corresponding to line X2-X2 ofFIG. 28 during the same step as FIG. 37. Herein, an insulating film(fourth insulating film) 9 made of, for example, silicon oxide is formedon the sides of the first electrodes 4G and the conductor film 4 by thethermal oxidation method. By forming the insulating film 9 with athermal oxide film having a good film quality, it is possible to improvethe withstand voltage between the first electrode 4G and the floatinggate electrode 6G. The thickness (the dimension along the directionparallel with the principal surface of the substrate 1S) of theinsulating film 9 is, for example, about 10 nm in terms of the silicondioxide equivalent film thickness. Whereas, by the thermal oxidationprocessing, the dimension along the second direction Y of the firstelectrode 4G becomes, for example, about 65 nm.

Subsequently, over the principal surface of the substrate 1S, aninsulating film made of, for example, silicon oxide is deposited by aCVD method using, for example, TEOS, and then, this is etched back. Thestate of the device after this step is shown in FIGS. 39 and 40. FIG. 39shows a cross sectional view of a portion corresponding to line Y1-Y1 ofFIG. 28 during the manufacturing step of the flash memory subsequent tothe manufacturing step of FIG. 37. FIG. 40 shows a cross sectional viewof a portion corresponding to line X2-X2 of FIG. 28 during the same stepas FIG. 39. By the etch back processing of the insulating film, thesidewall of the insulating film (fourth insulating film) 16 is formed onthe sides of the multilayered film of the first electrode 4G, the capfilm 10, and the insulating film 11. Whereas, at this step, the portionsof the insulating film 8 at the bottom of each trench 28 are removed toexpose the corresponding portions of the principal surface of thesubstrate 1S. Further, by the formation of the sidewall of theinsulating film 16, the dimension along the second direction Y (width)of the trench 28 becomes, for example, about 65 nm.

Herein, when the boron introducing steps shown in FIGS. 33 to 36 havenot been carried out, it is possible to carry out the boron introducingsteps after the formation of the insulating film 16 (sidewall in theperiphery). Also in this case, similarly, by setting the p type impurityconcentration of the substrate 1S under the first electrode 4Grelatively lower than the p type impurity concentration under thefloating gate electrode 6G, it is possible to set the threshold voltageof the first electrode 4G lower than the threshold voltage of thefloating gate electrode 6G.

FIG. 41 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 28 during a manufacturing step of the flash memorysubsequent to the manufacturing step in FIG. 39. FIG. 42 is a crosssectional view of a portion corresponding to line X1-X1 of FIG. 28during the same step as FIG. 41. FIG. 43 is a cross sectional view of aportion corresponding to line X2-X2 of FIG. 28 during the same step asFIG. 41. FIG. 44 shows a cross sectional view of one example of thesubstrate 1S in the peripheral circuit region of the flash memory duringthe same step as FIG. 33. Herein, first, the substrate 1S (wafer) issubjected to a thermal oxidation processing such as an ISSG oxidationmethod. As a result, an insulating film made of, for example, siliconoxide, is formed over the portions of the principal surface of thesubstrate 1S at the bottoms of the trenches 28. Then, a thermalprocessing (oxynitriding) is carried out in a gas atmosphere containingnitrogen (N). As a result, nitrogen is segregated in the interfacebetween the insulating film and the substrate 1S, thereby to form theinsulating film (fifth insulating film) 15 made of silicon oxynitride(SiON). The insulating film 15 is a film functioning as a tunnelinsulating film of the memory cells MC. The thickness is, for example,about 9 nm in terms of the silicon dioxide equivalent film thickness.Subsequently, a conductor film 6 made of, for example, a low resistivepolysilicon is deposited over the principal surface of the substrate 1Sby a CVD method or the like. At this step, the trenches 28 are fullyfilled with the conductor film 6, so that a “cavity” is prevented frombeing formed in each trench 28. In this embodiment 1, the side of eachtrench 28 is set as vertical as possible with respect to the principalsurface of the substrate 1S. This enables the conductor film 6 to besatisfactorily buried so that “a cavity” is prevented from being formedin the trench 28.

Subsequently, the conductor film 6 which is provided entirely over theprincipal surface of the substrate 1S is subjected to an etch backprocessing by an anisotropic dry etching processing, or a CMP (ChemicalMechanical Polishing) processing. The states of the device after theprocessing are shown in FIGS. 45 to 48. FIG. 45 is a cross sectionalview of a portion corresponding to line Y1-Y1 of FIG. 28 during amanufacturing step of the flash memory subsequent to the manufacturingstep of FIG. 41. FIG. 46 is a cross sectional view of a portioncorresponding to line X1-X1 of FIG. 28 during the same step as FIG. 45.FIG. 47 is a cross sectional view of a portion corresponding to lineX2-X2 of FIG. 28 during the same step as FIG. 45. FIG. 48 shows a crosssectional view of one example of the substrate 1S in the peripheralcircuit region of the flash memory during the same step as FIG. 45. Bythe etch back processing or the CMP processing, the portions of theconductor film 6 are left only in the trenches 28 (each hollow region ofFIGS. 27 and 28 as seen in a plan view). At this step, the depth of thepit from the top surface of the insulating film 11 to the top surface ofthe conductor film 6 is preferably set at, for example, about 30 nm orless.

FIG. 49 is a plan view showing one example of the substrate 1S during amanufacturing step of the flash memory subsequent to the manufacturingstep of FIG. 41. FIG. 50 is a cross sectional view taken along lineY1-Y1 of FIG. 49. FIG. 51 is a cross sectional view taken along lineX1-X1 of FIG. 49. FIG. 52 is a cross sectional view showing one exampleof the substrate 1S in the peripheral circuit region of the flash memoryduring the same step as FIG. 49. Herein, first, over the principalsurface of the substrate 1S (wafer), such a resist pattern RP3 as toexpose a memory region (region where a memory cell MC group is arranged)and to cover the other regions is formed. Then, by using this resistpattern as an etching mask, the portions of the insulating films 11 and16, exposed therefrom, are etched by a dry etching method or the like.At this step, the etch selectivity of silicon oxide to silicon andsilicon nitride is increased so that silicon oxide becomes more likelyto be removed than silicon and silicon nitride. This allows the cap film10 made of silicon nitride to function as an etching stopper, and inaddition, it allows the insulating films 11 and 16 made of silicon oxideto be selectively removed. At this step, when the etching residue of theinsulating film 16 is to be formed at a part of the side of theconductor film 6, a wet etching processing may be performed, thereby toremove the etching residue of the insulating film 16 made of siliconoxide. Then, the resist pattern RP3 is removed. Thus, in this embodiment1, the conductor film 6 for forming the floating gate electrodes isformed in self-alignment with the first electrodes 4G without using aphotomask. For this reason, it is possible to set the alignmentallowance between the conductor film 6 and the first electrodes 4Gsmaller than in the case where the conductor film 6 at this step isformed by a photolithography step using a photomask. Therefore, thememory cell MC can be reduced in size, and the chip size can be reduced.Further, it is possible to improve the alignment accuracy between theconductor film 6 and the first electrodes 4G. Accordingly, it ispossible to improve the electrical characteristics of the memory cellsMC. Still further, since the conductor film 6 is formed without using aphotomask, it is possible to omit a manufacturing step for a sheet of aphotomask. In addition, it is possible to omit a series ofphotolithography steps of coating, exposure, and development of aphotoresist film. For this reason, as compared with the case where theconductor film 6 at this step is formed by a photolithography step usinga photomask, it is possible to reduce the time required formanufacturing the flash memory, which can shorten the delivery time ofthe flash memory. In addition, it is possible to reduce the number ofphotomasks, which can reduce the cost of the flash memory. Trenches 29are formed between the portions of the conductor film 6 adjacent to eachother along the second direction Y of FIG. 49. In this embodiment 1, theside of the trench 28 is set as vertical as possible with respect to theprincipal surface of the substrate 1S. This also causes the side of thetrench 29 to be roughly as vertical as possible with respect to theprincipal surface of the substrate 1S.

FIG. 53 is a cross sectional view of a portion corresponding to lineY1-Y1 of FIG. 49 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 49. FIG. 54 is a crosssectional view of a portion corresponding to line X1-X1 of FIG. 49during the same step as FIG. 53. FIG. 55 is a cross sectional view of aportion corresponding to line X2-X2 of FIG. 49 during the same step asFIG. 53. FIG. 56 shows a cross sectional view one example of thesubstrate 1S in the peripheral circuit region of the flash memory duringthe same step as FIG. 53. Herein, first, over the principal surface ofthe substrate 1S (wafer), for example, an insulating film made ofsilicon oxide, an insulating film made of silicon nitride, and aninsulating film made of silicon oxide are sequentially deposited fromthe bottom layer by a CVD method or the like. As a result, an insulatingfilm for an interlayer film (sixth insulating film) 18 is formed. Thetop and bottom insulating films of the insulating film 18 which are madeof silicon oxide also can be formed by a thermal oxidation method suchas an ISSG oxidation method. In this case, it is possible to improve thefilm quality of the insulating film 18. Subsequently, over theinsulating film 18 of the substrate 1S, a conductor film 5 a made of,for example, a low resistive polysilicon, and a refractory metalsilicide film 5 b, such as a film of tungsten silicide serving as aconductor film 5 b that is lower in resistance than the conductor film 5a, are sequentially deposited from the lower layer by a CVD method orthe like. The conductor films 5 a and 5 b are patterned in thesubsequent step to form a word line 5 of memory cells MC. In thisembodiment 1, the side of each trench 29 is set as vertical as possiblewith respect to the principal surface of the substrate 1S. This enablesthe conductor film 5 a to be satisfactorily buried so that “a cavity” isprevented from being formed between the adjacent portions of theconductor film 6. The thickness of the conductor film 5 a is, forexample, about 100 to 150 nm. The thickness of the refractory metalsilicide film 5 b is, for example, about 100 nm. Subsequently, over therefractory metal silicide film 5 b, an insulating film 13 made of, forexample, silicon oxide is deposited by a CVD method using a TEOS gas, orthe like. Then, a hard mask film 26 b made of, for example, a lowresistive polysilicon is deposited thereon by a CVD method or the like.Further, an antireflection film 27 b made of, for example, siliconoxynitride (SiON) is deposited thereon by a CVD method or the like.

Then, over the antireflection film 27 b, a resist pattern for forming aword line is formed. By using this resist pattern as an etching mask,the antireflection film 27 b and the hard mask film 26 b are patterned.Then, the resist pattern for forming a word line is removed.Subsequently, by the use of the multilayered film of the left portionsof the hard mask film 26 b and the antireflection film 27 b as anetching mask, the portions of the insulating film 13, the refractorymetal silicide film 5 b, and the conductor film 5 a, exposed therefrom,are etched. The etching at this step is carried out in the same manneras used in the patterning step for the first electrodes. Whereas, forthe etching, the interlayer insulating film 18 is allowed to function asan etching stopper. Further, for example, when the trench 29 is in theform of an inverted taper, which may cause an etching residue of theconductor film 5 a to be left on the bottom side or the like of thetrench 29, it is possible to remove the etching residue of the conductorfilm 5 a by adding an isotropic etching processing, such as a wetetching method. The states of the device after such a step are shown inFIG. 57 to 61. FIG. 57 is a plan view showing the flash memory during amanufacturing step subsequent to the manufacturing step of FIG. 53. FIG.58 is a cross sectional view taken along line Y1-Y1 of FIG. 57. FIG. 59is a cross sectional view taken along line Y2-Y2 of FIG. 57. FIG. 60 isa cross sectional view taken along line X1-X1 of FIG. 57. FIG. 61 is across sectional view taken along line X2-X2 of FIG. 57. Herein, aplurality of word lines 5, each in the form of a band, as seen in planview, and extending in the second direction Y of FIG. 57, are formed bythe etching processing.

FIG. 62 is a plan view showing the flash memory during a manufacturingstep subsequent to the manufacturing step of FIG. 57. FIG. 63 is a crosssectional view taken along line Y1-Y1 of FIG. 62. FIG. 64 is a crosssectional view taken along line Y2-Y2 of FIG. 62. FIG. 65 is a crosssectional view taken along line X1 -X1 of FIG. 62. FIG. 66 is a crosssectional view taken along line X2-X2 of FIG. 62. FIG. 67 is a crosssectional view showing one example of the substrate 1S in the peripheralcircuit region of the flash memory during the same step as FIG. 62.Herein, first, over the principal surface of the substrate 1S (wafer),such a resist pattern RP4 as to expose a memory region and to cover theother regions is formed. Then, by using the resist pattern as an etchingmask, the portions of the insulating film 18 on the bottom of eachtrench 29 and the top of the conductor film 6 are etched. At this step,as shown in FIG. 64, the insulating film 18 on the side of the conductorfilm 6 may be lifted off by a washing processing or the like after theremoval processing of the conductor film 6, resulting in the formationof foreign matter. Such being the situation, in this embodiment 1, anoveretching processing is carried out to some degree at the time of theetching processing of the insulating film 18, thereby to remove the topportion of the insulating film 18 on the side of the conductor film 6.This causes the left insulating film 18 to be reduced in height, andmakes it resistant to being lifted off.

Subsequently, as shown in FIGS. 68 and 69, by the use of the word lines5 that have been formed in the foregoing manner as an etching mask, theportions of the conductor film 6 exposed therefrom are etched. FIG. 68is a cross sectional view of a portion corresponding to line Y2-Y2 ofFIG. 62 during the manufacturing step of the flash memory subsequent tothe manufacturing step of FIG. 62. FIG. 69 is a cross sectional view ofa portion corresponding to line X1-X1 of FIG. 62. Herein, by the etchingprocessing of the conductor film 6 using the word lines 5 as an etchingmask, floating gate electrodes 6G are formed in self-alignment with theword lines 5. Namely, the floating gate electrodes 6G are formed inself-alignment with both the first electrodes 4G and the word lines 5.Then, memory cells MC are formed in this manner. When floating gateelectrodes each in a concave form as seen in cross section are formed intrenches, the conductor film for the floating gate electrodes must bereduced in thickness with the reduction in size of memory cells MC.Therefore, the processing of the floating gate electrodes is difficult.In contrast, in this embodiment 1, each floating gate electrode 6G is ina convex form as seen in cross section. As a result, it is possible tocarry out the processing of the floating gate electrode 6G with easeeven when the memory cell MC has been reduced in size. Whereas, thefloating gate electrodes 6G are formed in self-alignment with both thefirst electrodes 4G and the word lines 5 without using a photomask. Forthis reason, it is possible to set the alignment allowance between thefloating gate electrodes 6G and the first electrodes 4G and the wordlines 5 smaller than in the case where the floating gate electrodes 6Gare formed by a photolithography step using a photomask. Therefore, thememory cell MC can be reduced in size, and the chip size can be reduced.Further, it is possible to improve the alignment accuracy between thefloating gate electrodes 6G and the first electrodes 4G and the wordlines 5. Accordingly, it is possible to improve the electricalcharacteristics of the memory cells MC. Still further, since thefloating gate electrodes 6G are formed without using a photomask, it ispossible to omit a manufacturing step of a sheet of a photomask (or twosheets of photomasks in a total number including the aforesaid one). Inaddition, it is possible to omit a series of photolithography steps ofcoating, exposure, and development of a photoresist film. For thisreason, as compared with the case where the floating gate electrodes 6Gare formed by a photolithography step using a photomask, it is possibleto reduce the time required for manufacturing the flash memory, whichcan shorten the delivery time of the flash memory. In addition, it ispossible to reduce the number of photomasks, which can reduce the costof the flash memory.

Thereafter, by a photolithography technique and a dry etching technique,the conductor film 4 for forming the first electrodes left in theperiphery of the memory region and in the peripheral circuit region ispatterned. As a result, as shown in FIGS. 70 and 71, wires 4LA and 4LC(4LC1), the gate electrodes 4A and 4B of the MIS in the peripheralcircuit, and the like are formed in the outer periphery of the memoryregion and the peripheral circuit region. FIG. 70 shows a crosssectional view of a portion corresponding to line X2-X2 of FIG. 62during a manufacturing step of the flash memory subsequent to themanufacturing step of FIG. 68. FIG. 71 shows a cross sectional view ofone example of the substrate 1S in the peripheral circuit region of theflash memory during the same step as FIG. 70.

As shown in FIGS. 72 to 74, an n⁻ type semiconductive region 22 b 1 forthe source and the drain of a selecting nMIS Qsn, an n⁻ typesemiconductive region 32 a for the source and the drain of an nMIS Qnfor the peripheral circuit, and a p⁻ type semiconductive region 33 a forthe source and the drain of a pMIS are respectively formed by separatesteps. Subsequently, over the principal surface of the substrate 1S(wafer), an insulating film made of silicon oxide or the like isdeposited by a CVD method using, for example, a TEOS gas, or the like.Then, the insulating film is etched back by an anisotropic dry etchingmethod. As a result, the insulating film 17 is buried in the gap betweenthe word lines 5 that are adjacent to each other, and between the firstelectrode 4G and the wire 4LA (4LB). In addition, sidewalls of theinsulating film 17 are formed on the one side surface of the outermostperipheral word line 5, the one side surface of the wire 4LC, and thesides of the gate electrodes 4A and 4B. Subsequently, an n⁺ typesemiconductive region 22 b 2 of the selecting nMIS Qsn, an n⁺ typesemiconductive region 32 b for the source and the drain of the nMIS Qnfor a peripheral circuit, and a p⁺ type semiconductive region 33 b forthe source and the drain of the pMIS are respectively formed by separatesteps. FIG. 72 shows a cross sectional view of a portion correspondingto line X1-X1 of FIG. 62 during a manufacturing step of the flash memorysubsequent to the manufacturing step of FIG. 70. FIG. 73 shows a crosssectional view of a portion corresponding to line X2-X2 of FIG. 62during the same step as FIG. 72. FIG. 74 shows a cross sectional view ofone example of the substrate 1S in the peripheral circuit region of theflash memory during the same step as FIG. 72. Thereafter, the flashmemory shown in FIGS. 1 to 4 is manufactured through conventional wireforming steps.

The reason why the side of the trench 28 has been set as vertical aspossible with respect to the principal surface of the substrate 1S willbe described. First, as shown in FIG. 75, in the case where an invertedtaper (the shape in which the aperture diameter of the trench 28gradually decreases from the bottom toward the top of the trench 28) isformed at the side of the trench 28, a cavity 35 is formed in theconductor film 6 in the trench 28 upon depositing the conductor film 6.When the insulating film 18 is formed as shown in FIG. 76 while still inthis state, the insulating film 18 is buried in the cavity 35. With thisbeing the situation, the unnecessary conductor film 6 is removed in thesubsequent step. As a result, as shown in FIGS. 77 and 78, theinsulating film 18 in the cavity 35 serves as a mask, so that theetching residue of the conductor film 6 resulting from the insulatingfilm 18 in the cavity 35 is generated between the word lines 5. As aresult, an electrical connection is established between the adjacentfloating gate electrodes 6G by the etching residue of the conductor film6. Incidentally, FIGS. 75 to 77 show cross sectional views duringrespective manufacturing steps of a portion corresponding to line Y2-Y2of FIG. 78. On the other hand, as shown in FIG. 79, when a forward taper(the shape in which the aperture diameter of the trench 28 graduallyincreases from the bottom toward the top of the trench 28) is formed atthe side of the trench 28, it is possible to satisfactorily bury theconductor film 6 without the formation of a “cavity” in the trench 28.However, as shown in FIG. 80, the trench 29 between the adjacentportions of the conductor film 6 is shaped in an inverted taper. Thisresults in the formation of a cavity 36 in the conductor film 5 in thetrench 29 during the subsequent deposition step of the conductor film 5a for a word line. When the word line 5 is processed with the cavity 36still in this state, the cavity 36 expands, as shown in FIG. 81. Forthis reason, it becomes difficult to process the word line 5. Further,the resistance of the word line 5 increases due to the cavity 36. All ofthese problems become noticeable with increased reduction in the size ofa memory cell MC, and, hence, this causes an inhibition of theadvancement of a desired reduction in the size of the memory cells MC.Such being the situation, in this embodiment 1, the side of the trench28 is formed as vertically as possible with respect to the principalsurface of the substrate 1S. As a result, it is possible to form memorycells MC without leaving the etching residue of the conductor film 6resulting from the cavity 35, and without causing problems in theprocessing of the word line 5 due to the cavity 36. Therefore, it ispossible to improve the reliability and the yield of the flash memory.Further, it is possible to promote the desired reduction in the size ofthe flash memory.

Embodiment 2

In this embodiment 2, a description will be given of the case where theplurality of first electrodes to which the same electric potential issupplied are disposed independently as with the other first electrodes,and are electrically connected through a different layer.

FIG. 82 shows one example as seen in plan view of a flash memoryrepresenting this embodiment 2. The first electrodes 4G are eachindependently arranged. The first electrodes 4G to which the sameelectric potential is supplied are electrically connected to one anotherby the upper layer wire through the contact holes CT.

The different points in manufacturing steps of the flash memory of thisembodiment 2 from the manufacturing steps of the flash memory of theembodiment 1 will be described by reference to FIGS. 83 to 85.Incidentally, FIGS. 83 to 85 are cross sectional views of a portioncorresponding to line X2-X2 of FIG. 82 during respective manufacturingsteps.

First, after the device has gone through the steps of FIGS. 10 to 69, asdescribed in connection with embodiment 1, as shown in FIG. 83, a partof the insulating film 18 in the outer periphery of the memory region isremoved by an etching processing. As a result, the conductor film 6 leftin the outer periphery of the memory region is exposed. Subsequently,the conductor film 6 in the outer periphery of the memory region isselectively removed by an etching processing, as shown in FIG. 84.Thereafter, as with the embodiment 1, the conductor film 4 left in theouter periphery of the memory region is patterned by a photolithographytechnique and a dry etching technique. This results in the formation ofthe wire 4LC (gate electrode 4LC1), as shown in FIG. 85. Then, a resistpattern RP5 covering the memory region is formed, and then, for example,arsenic is introduced into the substrate 1S (wafer) by a conventionalion implantation method. As a result, n⁻ type semiconductive regions 22a and 22 b 1 for forming the source/drain region of the selecting nMISQsn are formed. In addition, an n⁻ type semiconductive region 22 aconnecting the region (region where an inversion layer is formed) underthe first electrode 4G and the selecting MIS Qsn is formed. In thisembodiment 2, the n⁻ type semiconductive regions 22 a and 22 b 1 of theselecting nMIS Qsn, and the n⁻ type semiconductive region 7 forconnection can be formed by the same step. This enables a simplificationof the step. The subsequent steps are the same as those employed in theembodiment 1, and, hence, a description thereof is omitted.

Embodiment 3

In this embodiment 3, a description will be given for the case where thepresent invention has been applied to, for example, a flash memoryhaving an assist gate electrode.

A flash memory of this embodiment 3 is, for example, a 1-Gbit AG-AND(Assist Gate-AND) type flash memory. FIG. 86 shows a cross sectionalview of the memory region (the portion corresponding to line Y1-Y1 ofFIG. 1) of the flash memory of this embodiment 3.

In this embodiment 3, assist gate electrodes AG are disposed in place ofthe first electrodes 4G in the embodiments 1 and 2. In addition, in theprincipal surface portion of the substrate 1S, an n type semiconductiveregion 37 for forming a bit line is formed between each assist gateelectrode AG and each floating gate electrode 6G.

The assist gate electrodes AG are arranged in the same manner as thefirst electrodes 4G of FIG. 1. The assist gate electrodes AG have anisolating function for causing isolation between the selected memorycell and the non-selected memory cell. However, each assist gateelectrode AG does not form an n type inversion layer for forming a bitline in the substrate 1S, but it has a function of assisting the writingof data at a high speed and with a low channel current by efficientlygenerating hot electrons and injecting them into the floating gateelectrode 6G for the data write operation. Namely, for the data writeoperation, the channel under the assist gate electrode AG is weaklyinverted, and the channel under the floating gate electrode 6G iscompletely depleted. A large potential drop is caused at the interfacebetween the assist gate electrode AG and the floating gate electrode 6G.This results in an increase in the electric field along the lateraldirection of the channel at the interface. As a result, it is possibleto form hot electrons with efficiency. This can implement high-speedwriting at a low channel current.

The n type semiconductive region 37 is a region for forming a bit line.Namely, the n type semiconductive region 37 is a region for forming thesource or the drain of the memory cell MC. Also, in this embodiment 3,the device is configured such that the semiconductive regions 37 for thesource and the drain of the mutually adjacent memory cells MC areshared. This enables a reduction of the area occupied by the memoryregion. The n type semiconductive region 37 is formed in such a manneras to extend along the direction of extension (the first direction X ofFIG. 1) of the assist gate electrode AG. The n type semiconductiveregion 37 is formed in the following manner. For example, before orafter the introduction of boron in the steps (the steps of introducingboron in order to cause a difference between the threshold voltage underthe first electrode 4G and the threshold voltage under the floating gateelectrode 6G) of FIGS. 33 to 35 in the embodiment 1, for example,impurity ions of phosphorus, arsenic, or the like are introduced fromthe direction oblique with respect to the principal surface of thesubstrate 1S. Alternatively, the semiconductive region 37 may also beformed in the following manner. For example, after the formation of thesidewall of the insulating film 16 as described in connection with FIGS.39 and 40 of the embodiment 1, impurity ions of, for example, phosphorusor arsenic are introduced from a direction oblique with respect to theprincipal surface of the substrate 1S. In accordance with such anembodiment 3, it is possible to obtain the same effects as with theembodiments 1 and 2. In addition, the n type semiconductive region 37 isdisposed as a bit line, and hence, it is possible to reduce theresistance of the bit line as compared with the embodiments 1 and 2.

Now, a description will be given with respect to write, read, anderasing operations of the flash memory of this embodiment 3.

FIG. 87 shows a cross sectional view of the substrate 1S during the datawrite operation by the constant charge injection of the flash memory ofthis embodiment 3. For the data write operation, the word line 5 towhich the selected memory cell MC is connected is supplied with avoltage of, for example, about 15 V. The other word lines 5 or the likeare supplied with a voltage of, for example, 0 V. Whereas, the assistgate electrode AG0 between the source of the selected memory cell MC andthe floating gate electrode 6G is supplied with a voltage of, forexample, 1 V. The assist gate electrode AG1 on the drain side of theselected memory cell MC is supplied with, for example, about 0 V. Theother assist gate electrodes AG2 and AG3 are supplied with a voltage of,for example, 0V. Thus, the isolation is caused between the selected andnon-selected memory cells MC. In this state, to the n typesemiconductive region 37 a on the source side, for example, 0V issupplied. Whereas, to the n type semiconductive region 37 b on the drainside, a voltage of, for example, about 4 V is supplied. This causes awrite current to flow from the drain toward the source in the selectedmemory cell MC. The electric charges accumulated in the n typesemiconductive region 37 b at this step are allowed to flow as aconstant channel current, and they are injected into the floating gateelectrode 6G with efficiency via the insulating film 15 (constant chargeinjection method). Thus, data is written to the selected memory cell MC.

FIG. 88 shows a cross sectional view of the substrate 1S during the dataread operation of the flash memory of this embodiment 3. For the dataread operation, the word line 5 to which the selected memory cell MC isconnected is supplied with a voltage of, for example, about 2 to 5 V.The other word lines 5 or the like are supplied with a voltage of, forexample, 0 V. Whereas, the assist gate electrode AG0 between the sourceof the selected memory cell MC and the floating gate electrode 6G issupplied with a voltage of, for example, about 3.5 V. The assist gateelectrode AG1 on the drain side of the selected memory cell MC issupplied with, for example, about 0 V. The other assist gate electrodesAG2 and AG3 are supplied with a voltage of, for example, 0V. Thus,isolation is created between the selected and non-selected memory cellsMC. In this state, to the n type semiconductive region 37 a on thesource side, for example, a voltage of 0 V is supplied. Whereas, to then type semiconductive region 37 b on the drain side, a voltage of, forexample, about 1 V is supplied. At this step, the conditions of theaccumulated electric charges of the floating gate electrode 6G changethe threshold voltage of the selected memory cell MC. For this reason,it is possible to judge the data of the selected memory cell MCaccording to the conditions of the current flowing between the sourceand the drain of the selected memory cell MC.

FIG. 89 shows a cross sectional view of the substrate 1S during the dataerasing operation of the flash memory of this embodiment 3. The dataerasing operation is the same as that of embodiment 1. Namely, the wordline 5 to be selected is supplied with a voltage of, for example, about−16 V. On the other hand, the n type semiconductive regions 37 a and 37b are supplied with a voltage of, for example, 0V. This causes theelectric charges for data accumulated in the floating gate electrode 6Gto be emitted into the substrate 1S via the insulating film 15. Thus,the data of a plurality of the memory cells MC are erased by oneoperation.

Embodiment 4

In connection with this embodiment 4, a description will be given to,for example, a modified example of a flash memory having an assist gateelectrode.

A flash memory of this embodiment 4 is, for example, a 1-Gbit AG-ANDtype flash memory. FIG. 90 shows a cross sectional view of a memoryregion (a portion corresponding to line Y1-Y1 of FIG. 1) of the flashmemory of this embodiment 4. In this embodiment 4, the n typesemiconductive regions 37 are arranged at every other assist gateelectrodes AG, and they are disposed immediately under the assist gateelectrodes AG. The n type semiconductive regions 37 may be formed in thefollowing manner. For example, after the steps (the steps of removingthe insulating film 11 between the portions of the conductor films 6,and the like) of FIGS. 49 to 52 of the embodiment 1, a resist pattern isformed to expose the formation region of the n type semiconductiveregion 37, and to cover the other regions. By the use of this resistpattern as a mask, impurity ions such as phosphorus ions or arsenic ionsare introduced vertically with respect to the principal surface of thesubstrate 1S via the cap film 10 and the assist gate electrodes AG. Theassist gate electrodes AG under which the n type semiconductive regionsare not disposed have, other than the function as the assist gate, afunction of forming an n type inversion layer for a bit line in theprincipal surface of the substrate 1S for the read operation of thememory cell, as will be described later. In such an embodiment 4, the ntype semiconductive regions 37 are formed in such a manner as to bearranged under every other assist gate electrode AG, and they are formedso as not to extend under the floating gate electrodes 6G. For thisreason, even when the n type semiconductive regions 37 each slightlyexpand, it is possible to reduce the size of each memory cell MC.Whereas, the n type semiconductive regions 37 are formed as bit lines,and hence, it is possible to reduce the resistance of the bit lines ascompared with the embodiments 1 and 2.

Now, a description will be given with respect to write, read, anderasing operations of the flash memory of this embodiment 4.

FIG. 91 shows a cross sectional view of the substrate 1S during the datawrite operation by the constant charge injection of the flash memory ofthis embodiment 4. For the data write operation, the word line 5 towhich the selected memory cell MC is connected is supplied with avoltage of, for example, about 15 V. The other word lines 5 or the likeare supplied with a voltage of, for example, 0 V. Whereas, the assistgate electrode AG0 between the source of the selected memory cell MC andthe floating gate electrode 6G is supplied with a voltage of, forexample, 1 V. The assist gate electrode AG1 on the drain side of theselected memory cell MC is supplied with, for example, about 0 V. Theother assist gate electrodes AG2 and AG3 are supplied with a voltage of,for example, 0V. Thus, isolation is created between the selected andnon-selected memory cells MC. In this state, to the n typesemiconductive region 37 for a source immediately under the assist gateelectrode AG3, a voltage of, for example, 0 V is supplied. Whereas, tothe n type semiconductive region 37 b for a drain immediately under theassist gate electrode AG1, a voltage of, for example, about 4 V issupplied. As a result, as with the embodiment 3, the electric chargesaccumulated in the n type semiconductive region 37 a on the source sideare injected into the floating gate electrode 6G with efficiency via theinsulating film 15. Thus, data is written to the selected memory cell MCat a high speed.

FIG. 92 shows a cross sectional view of the substrate 1S during the dataread operation of the flash memory of this embodiment 4. For datareading, the word line 5 to which the selected memory cell MC isconnected is supplied with a voltage of, for example, about 2 to 5 V.The other word lines 5 or the like are supplied with a voltage of, forexample, 0 V. Whereas, the assist gate electrode AG0 is supplied with avoltage of, for example, about 5 V, thereby to form an n type inversionlayer 23 c for a source in the principal surface of the substrate 1S,opposing thereto. The other assist gate electrodes AG1 and AG3 aresupplied with a voltage of, for example, 0V. Thus, isolation is providedbetween the selected and non-selected memory cells MC. In this state, tothe n type inversion layer 23 c on the source side, for example, avoltage of 0 V is supplied. Whereas, to the semiconductive region 37 bfor a drain, a voltage of, for example, about 1 V is supplied. At thisstep, the conditions of the accumulated electric charges of the floatinggate electrode 6G change the threshold voltage of the selected memorycell MC. For this reason, it is possible to judge the data of theselected memory cell MC according to the conditions of the currentflowing between the source and the drain of the selected memory cell MC.

FIG. 93 shows a cross sectional view of the substrate 1S during the dataerasing operation of the flash memory of this embodiment 4. The dataerasing operation is the same as that of the embodiment 1. Namely, theword line 5 to be selected is supplied with a voltage of, for example,about −16 V. On the other hand, the assist gate electrodes AG0 to AG3are supplied with a voltage of, for example, 0V. This causes theelectric charges for data accumulated in the floating gate electrode 6Gto be emitted into the substrate 1S via the insulating film 15. Thus,the data of a plurality of the memory cells MC are erased by oneoperation.

Up to this point, the aspects of the invention completed by the presentinventors have been described specifically by way of exemplaryembodiments. However, the present invention is not limited to theembodiments described herein, and it is understood that various changesmay made within a range not departing from the scope thereof.

In the foregoing explanation, a description was given of the case wherethe invention completed by the present inventors was applied to an ANDtype flash memory unit in the field which has formed the backgroundthereof. However, the present invention is not limited thereto, and itis also applicable to a memory-merged semiconductor device, such as asemiconductor device of an EEPROM unit or a system LSI (Large ScaleIntegrated circuit) having an EEPROM or a flash memory.

The effects obtainable with typical aspects and features of theinvention disclosed herein will be briefly described as follows. Namely,a semiconductor device comprises, a semiconductor substrate; and aplurality of nonvolatile memory cells having a plurality of firstelectrodes, a plurality of second electrodes provided so as to crosstherewith, and a plurality of third electrodes for electric chargeaccumulation provided at points of intersection of the portions betweenthe plurality of the adjacent first electrodes and the plurality of thesecond electrodes in a state insulated from the first and secondelectrodes over the semiconductor substrate, wherein the thirdelectrodes are formed in a convex shape as seen in cross section in sucha manner as to be larger in height than the first electrodes. Thisenables a reduction in the size of the semiconductor device.

Further, a semiconductor device comprises, a semiconductor substrate;and a plurality of nonvolatile memory cells having a plurality of firstelectrodes, a plurality of second electrodes provided so as to crosstherewith, and a plurality of third electrodes for electric chargeaccumulation provided at points of intersection of the portions betweenthe plurality of the adjacent first electrodes and the plurality of thesecond electrodes in a state insulated from the first and secondelectrodes over the semiconductor substrate, wherein the plurality offirst electrodes have a function of forming an inversion layer in thesemiconductor substrate. This can promote the trend toward reduction inthe size of the nonvolatile memory. Further, it is possible to reducethe size of the semiconductor device.

The semiconductor device of the present invention is applicable to asemiconductor device having a nonvolatile semiconductor memory such asan EEPROM or a flash memory.

1. A method of manufacturing a semiconductor device comprising: asemiconductor substrate; and a plurality of nonvolatile memory cellshaving a plurality of first electrodes provided over the semiconductorsubstrate, a plurality of second electrodes provided over thesemiconductor substrate so as to cross with the plurality of the firstelectrodes, and a plurality of third electrodes for electric chargeaccumulation provided at positions which respectively lie between theplurality of the adjacent first electrodes and overlap with theplurality of the second electrodes in plan view, the method comprisingthe steps of: (a) depositing a conductor film for forming the firstelectrodes over the semiconductor substrate via a first insulating film;(b) depositing a second insulating film over the conductor film forforming the first electrodes; (c) depositing a third insulating filmover the second insulating film; (d) patterning the conductor film forforming the first electrodes, the second insulating film, and the thirdinsulating film, thereby to form a multilayered pattern of the firstelectrodes, the second insulating film, and the third insulating film;(e) forming a fourth insulating film over the sides of the firstelectrodes; (f) forming a fifth insulating film over the parts of thesemiconductor substrate between the adjacent portions of themultilayered pattern of the first electrodes, the second insulatingfilm, and the third insulating film; (g) depositing a conductor film forforming the third electrodes over the semiconductor substrate such thatthe parts between the adjacent portions of the multilayered pattern ofthe first electrodes, the second insulating film, and the thirdinsulating film are buried; (h) removing the conductor film for formingthe third electrodes such that the portions of the conductor film forforming the third electrodes are left between the adjacent portions ofthe multilayered pattern of the first electrodes, the second insulatingfilm, and the third insulating film, thereby to form a pattern of theconductor film for forming the third electrodes between the adjacentportions of the multilayered pattern of the first electrodes, the secondinsulating film, and the third insulating film in self-alignment withthe first electrodes; (i) removing the third insulating film; (j)depositing a sixth insulating film over the semiconductor substrate; (k)depositing a conductor film for forming the second electrodes over thesixth insulating film; (l) patterning the conductor film for forming thesecond electrodes, thereby to form the plurality of the secondelectrodes; and (m) patterning the pattern of the conductor film forforming the third electrodes by the use of the plurality of the secondelectrodes as a mask, thereby to form the plurality of the thirdelectrodes in such a convex shape in cross section as to be larger inheight than the first electrodes in self-alignment with the plurality ofthe second electrodes.
 2. The method of manufacturing a semiconductordevice according to claim 1, further comprising, after the step (d) or(e), and before the step (f), a step of introducing a desired impurityfrom an oblique direction with respect to the principal surface of thesemiconductor substrate, thereby to form, in the semiconductorsubstrate, a semiconductive region for a bit line of a conductivity typeopposite to the conductivity type of the semiconductor substrate.
 3. Themethod of manufacturing a semiconductor device according to claim 1,further comprising, after the step (i), and before the step (j), a stepof selectively introducing a desired impurity into the semiconductorsubstrate, thereby to form, in the semiconductor substrate, asemiconductive region for a bit line of a conductivity type opposite tothe conductivity type of the semiconductor substrate.
 4. The method ofmanufacturing a semiconductor device according to claim 1, wherein, forthe step (h), the conductor film for forming the third electrodes overthe entire surface of the semiconductor substrate is subjected to anetch back processing by an anisotropic dry etching processing, orsubjected to a chemical mechanical polishing processing.
 5. The methodof manufacturing a semiconductor device according to claim 1, whereinthe fourth insulating film in the step (e) includes a silicon oxide filmformed by a thermal oxidation method.
 6. The method of manufacturing asemiconductor device according to claim 1, wherein the second insulatingfilm is formed with silicon nitride, the third insulating film is formedwith silicon oxide, and in the step of removing the third insulatingfilm of the step (i), an etching processing is performed such that thesecond insulating film serves as an etching stopper.
 7. The method ofmanufacturing a semiconductor device according to claim 1, wherein, inthe step of patterning the conductor film for forming the secondelectrodes of the step (l), an etching processing is performed such thatthe sixth insulating film serves as an etching stopper.
 8. The method ofmanufacturing a semiconductor device according to claim 1, furthercomprising, after the step (d) or (e), and before the step (f), a stepof introducing a desired impurity into the portions of the semiconductorsubstrate between the adjacent portions of the multilayered pattern ofthe first electrodes, the second insulating film, and the thirdinsulating film such that the threshold voltage of the parts of theprincipal surface portion of the semiconductor substrate facing theplurality of the first electrodes is lower than the threshold voltage ofthe parts of the principal surface portion of the semiconductorsubstrate facing the plurality of the third electrodes.
 9. The method ofmanufacturing a semiconductor device according to claim 1, furthercomprising a step of patterning the conductor film for forming the firstelectrodes, thereby to form gate electrodes of field effect transistorsover the semiconductor substrate.
 10. The method of manufacturing asemiconductor device according to claim 1, the semiconductor devicefurther comprising field effect transistors for selecting the pluralityof the nonvolatile memory cells, the method further comprising the stepsof: (n) with a part of the conductor film for forming the firstelectrodes to be patterned in the step (d) left until after the step (m)for forming the gate electrodes of the field effect transistors for theselection, after the step (m), patterning the left conductor film forforming the first electrodes, thereby to form the gate electrodes of thefield effect transistors for the selection; and (o) after the step (n),introducing an impurity into the semiconductor substrate in alignmentwith the gate electrodes of the field effect transistors for theselection, thereby to form the source/drain regions of the field effecttransistors for the selection, wherein, before the step (a), an impurityis introduced in the semiconductor substrate, thereby to formsemiconductive regions for connecting the plurality of the nonvolatilememory cells and the field effect transistors for the selection.
 11. Themethod of manufacturing a semiconductor device according to claim 1, thesemiconductor device further comprising field effect transistors forselecting the plurality of the nonvolatile memory cells, the methodfurther comprising the steps of: (p) with a part of the conductor filmfor forming the first electrodes to be patterned in the step (d) leftuntil after the step (m) for forming the gate electrodes of the fieldeffect transistors for the selection, after the step (m), patterning theleft conductor film for forming the first electrodes, thereby to formthe gate electrodes of the field effect transistors for the selection;and (q) after the step (n), introducing an impurity into thesemiconductor substrate in alignment with the gate electrodes of thefield effect transistors for the selection, thereby to form thesource/drain regions of the field effect transistors for the selectionand the semiconductive regions for connecting the plurality of thenonvolatile memory cells with the field effect transistors for theselection.
 12. The method of manufacturing a semiconductor deviceaccording to claim 1, wherein the plurality of the third electrodes areformed so as to have a larger height than each length of the thirdelectrodes in a direction in which the second electrodes extend.
 13. Themethod of manufacturing a semiconductor device according to claim 1,wherein the plurality of the third electrodes are formed so as to have alarger height than the spacing between the plurality of the thirdelectrodes in a direction in which the second electrodes extend.
 14. Themethod of manufacturing a semiconductor device according to claim 1,wherein the third electrodes are formed each in the shape of a pole. 15.A method of manufacturing a semiconductor device comprising asemiconductor substrate, and a plurality of nonvolatile memory cellshaving a plurality of first electrodes provided over the semiconductorsubstrate, a plurality of second electrodes provided over thesemiconductor substrate so as to cross with the plurality of the firstelectrodes, and a plurality of third electrodes for electric chargeaccumulation provided at positions which respectively lie between theplurality of the adjacent first electrodes and overlap with theplurality of the second electrodes in plan view, the method comprisingthe steps of: (a) depositing a conductor film for forming the firstelectrodes over the semiconductor substrate via a first insulating film;(b) depositing a second insulating film over the conductor film forforming the first electrodes; (c) depositing a third insulating filmover the second insulating film; (d) patterning the conductor film forforming the first electrodes, the second insulating film, and the thirdinsulating film, thereby to form a multilayered pattern of the firstelectrodes, the second insulating film, and the third insulating film;(e) forming a fourth insulating film over the sides of the firstelectrodes; (f) forming a fifth insulating film over the parts of thesemiconductor substrate between the adjacent portions of themultilayered pattern of the first electrodes, the second insulatingfilm, and the third insulating film; (g) depositing a conductor film forforming the third electrodes over the semiconductor substrate such thatthe parts between the adjacent portions of the multilayered pattern ofthe first electrodes, the second insulating film, and the thirdinsulating film are buried; (h) removing the conductor film for formingthe third electrodes such that the portions of the conductor film forforming the third electrodes are left between the adjacent portions ofthe multilayered pattern of the first electrodes, the second insulatingfilm, and the third insulating film, thereby to form a pattern of theconductor film for forming the third electrodes between the adjacentportions of the multilayered pattern of the first electrodes, the secondinsulating film, and the third insulating film in self-alignment withthe first electrodes; (i) removing the third insulating film; (j)depositing a sixth insulating film over the semiconductor substrate; (k)depositing a conductor film for forming the second electrodes over thesixth insulating film; (l) patterning the conductor film for forming thesecond electrodes, thereby to form the plurality of the secondelectrodes; and (m) patterning the pattern of the conductor film forforming the third electrodes by the use of the plurality of the secondelectrodes as a mask, thereby to form the plurality of the thirdelectrodes in self-alignment with the plurality of the secondelectrodes, wherein the plurality of the first electrodes have afunction of forming an inversion layer in the semiconductor substrate.16. The method of manufacturing a semiconductor device according toclaim 15, further comprising, after the step (d) or (e), and before thestep (f), a step of introducing a desired impurity into the portions ofthe semiconductor substrate between the adjacent portions of themultilayered pattern of the first electrodes, the second insulatingfilm, and the third insulating film such that the threshold voltage ofthe parts of the principal surface portion of the semiconductorsubstrate facing the plurality of the first electrodes is lower than thethreshold voltage of the parts of the principal surface portion of thesemiconductor substrate facing the plurality of the third electrodes.17. The method of manufacturing a semiconductor device according toclaim 15, the semiconductor device further comprising field effecttransistors for selecting the plurality of the nonvolatile memory cells,the method further comprising the steps of: (n) with a part of theconductor film for forming the first electrodes to be patterned in thestep (d) left until after the step (m) for forming the gate electrodesof the field effect transistors for the selection, after the step (m),patterning the left conductor film for forming the first electrodes,thereby to form the gate electrodes of the field effect transistors forthe selection; and (o) after the step (n), introducing an impurity intothe semiconductor substrate in alignment with the gate electrodes of thefield effect transistors for the selection, thereby to form thesource/drain regions of the field effect transistors for the selection,wherein, before the step (a), an impurity is introduced in thesemiconductor substrate, thereby to form semiconductive regions forconnecting the plurality of the nonvolatile memory cells with the fieldeffect transistors for the selection.
 18. The method of manufacturing asemiconductor device according to claim 15, the semiconductor devicefurther comprising field effect transistors for selecting the pluralityof the nonvolatile memory cells, the method further comprising the stepsof: (p) with a part of the conductor film for forming the firstelectrodes to be patterned in the step (d) left until after the step (m)for forming the gate electrodes of the field effect transistors for theselection, after the step (m), patterning the left conductor film forforming the first electrodes, thereby to form the gate electrodes of thefield effect transistors for the selection; and (q) after the step (n),introducing an impurity into the semiconductor substrate in alignmentwith the gate electrodes of the field effect transistors for theselection, thereby to form the source/drain regions of the field effecttransistors for the selection and the semiconductive regions forconnecting the plurality of the nonvolatile memory cells and the fieldeffect transistors for the selection.
 19. The method of manufacturing asemiconductor device according to claim 15, wherein the plurality of thethird electrodes are formed so as to have a larger height than eachlength of the third electrodes in a direction in which the secondelectrodes extend.
 20. The method of manufacturing a semiconductordevice according to claim 15, wherein the plurality of the thirdelectrodes are formed so as to have a larger height than the spacingbetween the plurality of the third electrodes in a direction in whichthe second electrodes extend.
 21. The method of manufacturing asemiconductor device according to claim 15, wherein the third electrodesare formed each in the shape of a pole.